Refactor to move options to separate file

2 files changed, 1429 insertions, 1422 deletions

diff --git a/src/configuration.rs b/src/configuration.rs
new file mode 100644
index 0000000..3e8823d
--- /dev/null
+++ b/src/configuration.rs
@@ -0,0 +1,1421 @@
+use crate::util::{
+    line_ending::LineEnding,
+    mdx::{EsmParse as MdxEsmParse, ExpressionParse as MdxExpressionParse},
+};
+use alloc::{boxed::Box, fmt, string::String};
+
+/// Control which constructs are enabled.
+///
+/// Not all constructs can be configured.
+/// Notably, blank lines and paragraphs cannot be turned off.
+///
+/// ## Examples
+///
+/// ```
+/// use markdown::Constructs;
+/// # fn main() {
+///
+/// // Use the default trait to get `CommonMark` constructs:
+/// let commonmark = Constructs::default();
+///
+/// // To turn on all of GFM, use the `gfm` method:
+/// let gfm = Constructs::gfm();
+///
+/// // Or, mix and match:
+/// let custom = Constructs {
+///   math_flow: true,
+///   math_text: true,
+///   ..Constructs::gfm()
+/// };
+/// # }
+/// ```
+#[allow(clippy::struct_excessive_bools)]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Constructs {
+    /// Attention.
+    ///
+    /// ```markdown
+    /// > | a *b* c **d**.
+    ///       ^^^   ^^^^^
+    /// ```
+    pub attention: bool,
+    /// Autolink.
+    ///
+    /// ```markdown
+    /// > | a <https://example.com> b <user@example.org>.
+    ///       ^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^
+    /// ```
+    pub autolink: bool,
+    /// Block quote.
+    ///
+    /// ```markdown
+    /// > | > a
+    ///     ^^^
+    /// ```
+    pub block_quote: bool,
+    /// Character escape.
+    ///
+    /// ```markdown
+    /// > | a \* b
+    ///       ^^
+    /// ```
+    pub character_escape: bool,
+    /// Character reference.
+    ///
+    /// ```markdown
+    /// > | a &amp; b
+    ///       ^^^^^
+    /// ```
+    pub character_reference: bool,
+    /// Code (indented).
+    ///
+    /// ```markdown
+    /// > |     a
+    ///     ^^^^^
+    /// ```
+    pub code_indented: bool,
+    /// Code (fenced).
+    ///
+    /// ```markdown
+    /// > | ~~~js
+    ///     ^^^^^
+    /// > | console.log(1)
+    ///     ^^^^^^^^^^^^^^
+    /// > | ~~~
+    ///     ^^^
+    /// ```
+    pub code_fenced: bool,
+    /// Code (text).
+    ///
+    /// ```markdown
+    /// > | a `b` c
+    ///       ^^^
+    /// ```
+    pub code_text: bool,
+    /// Definition.
+    ///
+    /// ```markdown
+    /// > | [a]: b "c"
+    ///     ^^^^^^^^^^
+    /// ```
+    pub definition: bool,
+    /// Frontmatter.
+    ///
+    /// ````markdown
+    /// > | ---
+    ///     ^^^
+    /// > | title: Neptune
+    ///     ^^^^^^^^^^^^^^
+    /// > | ---
+    ///     ^^^
+    /// ````
+    pub frontmatter: bool,
+    /// GFM: autolink literal.
+    ///
+    /// ```markdown
+    /// > | https://example.com
+    ///     ^^^^^^^^^^^^^^^^^^^
+    /// ```
+    pub gfm_autolink_literal: bool,
+    /// GFM: footnote definition.
+    ///
+    /// ```markdown
+    /// > | [^a]: b
+    ///     ^^^^^^^
+    /// ```
+    pub gfm_footnote_definition: bool,
+    /// GFM: footnote label start.
+    ///
+    /// ```markdown
+    /// > | a[^b]
+    ///      ^^
+    /// ```
+    pub gfm_label_start_footnote: bool,
+    ///
+    /// ```markdown
+    /// > | a ~b~ c.
+    ///       ^^^
+    /// ```
+    pub gfm_strikethrough: bool,
+    /// GFM: table.
+    ///
+    /// ```markdown
+    /// > | | a |
+    ///     ^^^^^
+    /// > | | - |
+    ///     ^^^^^
+    /// > | | b |
+    ///     ^^^^^
+    /// ```
+    pub gfm_table: bool,
+    /// GFM: task list item.
+    ///
+    /// ```markdown
+    /// > | * [x] y.
+    ///       ^^^
+    /// ```
+    pub gfm_task_list_item: bool,
+    /// Hard break (escape).
+    ///
+    /// ```markdown
+    /// > | a\
+    ///      ^
+    ///   | b
+    /// ```
+    pub hard_break_escape: bool,
+    /// Hard break (trailing).
+    ///
+    /// ```markdown
+    /// > | a␠␠
+    ///      ^^
+    ///   | b
+    /// ```
+    pub hard_break_trailing: bool,
+    /// Heading (atx).
+    ///
+    /// ```markdown
+    /// > | # a
+    ///     ^^^
+    /// ```
+    pub heading_atx: bool,
+    /// Heading (setext).
+    ///
+    /// ```markdown
+    /// > | a
+    ///     ^^
+    /// > | ==
+    ///     ^^
+    /// ```
+    pub heading_setext: bool,
+    /// HTML (flow).
+    ///
+    /// ```markdown
+    /// > | <div>
+    ///     ^^^^^
+    /// ```
+    pub html_flow: bool,
+    /// HTML (text).
+    ///
+    /// ```markdown
+    /// > | a <b> c
+    ///       ^^^
+    /// ```
+    pub html_text: bool,
+    /// Label start (image).
+    ///
+    /// ```markdown
+    /// > | a ![b](c) d
+    ///       ^^
+    /// ```
+    pub label_start_image: bool,
+    /// Label start (link).
+    ///
+    /// ```markdown
+    /// > | a [b](c) d
+    ///       ^
+    /// ```
+    pub label_start_link: bool,
+    /// Label end.
+    ///
+    /// ```markdown
+    /// > | a [b](c) d
+    ///         ^^^^
+    /// ```
+    pub label_end: bool,
+    /// List items.
+    ///
+    /// ```markdown
+    /// > | * a
+    ///     ^^^
+    /// ```
+    pub list_item: bool,
+    /// Math (flow).
+    ///
+    /// ```markdown
+    /// > | $$
+    ///     ^^
+    /// > | \frac{1}{2}
+    ///     ^^^^^^^^^^^
+    /// > | $$
+    ///     ^^
+    /// ```
+    pub math_flow: bool,
+    /// Math (text).
+    ///
+    /// ```markdown
+    /// > | a $b$ c
+    ///       ^^^
+    /// ```
+    pub math_text: bool,
+    /// MDX: ESM.
+    ///
+    /// ```markdown
+    /// > | import a from 'b'
+    ///     ^^^^^^^^^^^^^^^^^
+    /// ```
+    ///
+    /// > 👉 **Note**: to support ESM, you *must* pass
+    /// > [`mdx_esm_parse`][MdxEsmParse] in [`ParseOptions`][] too.
+    /// > Otherwise, ESM is treated as normal markdown.
+    pub mdx_esm: bool,
+    /// MDX: expression (flow).
+    ///
+    /// ```markdown
+    /// > | {Math.PI}
+    ///     ^^^^^^^^^
+    /// ```
+    ///
+    /// > 👉 **Note**: You *can* pass
+    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
+    /// > too, to parse expressions according to a certain grammar (typically,
+    /// > a programming language).
+    /// > Otherwise, expressions are parsed with a basic algorithm that only
+    /// > cares about braces.
+    pub mdx_expression_flow: bool,
+    /// MDX: expression (text).
+    ///
+    /// ```markdown
+    /// > | a {Math.PI} c
+    ///       ^^^^^^^^^
+    /// ```
+    ///
+    /// > 👉 **Note**: You *can* pass
+    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
+    /// > too, to parse expressions according to a certain grammar (typically,
+    /// > a programming language).
+    /// > Otherwise, expressions are parsed with a basic algorithm that only
+    /// > cares about braces.
+    pub mdx_expression_text: bool,
+    /// MDX: JSX (flow).
+    ///
+    /// ```markdown
+    /// > | <Component />
+    ///     ^^^^^^^^^^^^^
+    /// ```
+    ///
+    /// > 👉 **Note**: You *must* pass `html_flow: false` to use this,
+    /// > as it’s preferred when on over `mdx_jsx_flow`.
+    ///
+    /// > 👉 **Note**: You *can* pass
+    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
+    /// > too, to parse expressions in JSX according to a certain grammar
+    /// > (typically, a programming language).
+    /// > Otherwise, expressions are parsed with a basic algorithm that only
+    /// > cares about braces.
+    pub mdx_jsx_flow: bool,
+    /// MDX: JSX (text).
+    ///
+    /// ```markdown
+    /// > | a <Component /> c
+    ///       ^^^^^^^^^^^^^
+    /// ```
+    ///
+    /// > 👉 **Note**: You *must* pass `html_text: false` to use this,
+    /// > as it’s preferred when on over `mdx_jsx_text`.
+    ///
+    /// > 👉 **Note**: You *can* pass
+    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
+    /// > too, to parse expressions in JSX according to a certain grammar
+    /// > (typically, a programming language).
+    /// > Otherwise, expressions are parsed with a basic algorithm that only
+    /// > cares about braces.
+    pub mdx_jsx_text: bool,
+    /// Thematic break.
+    ///
+    /// ```markdown
+    /// > | ***
+    ///     ^^^
+    /// ```
+    pub thematic_break: bool,
+}
+
+impl Default for Constructs {
+    /// `CommonMark`.
+    ///
+    /// `CommonMark` is a relatively strong specification of how markdown
+    /// works.
+    /// Most markdown parsers try to follow it.
+    ///
+    /// For more information, see the `CommonMark` specification:
+    /// <https://spec.commonmark.org>.
+    fn default() -> Self {
+        Self {
+            attention: true,
+            autolink: true,
+            block_quote: true,
+            character_escape: true,
+            character_reference: true,
+            code_indented: true,
+            code_fenced: true,
+            code_text: true,
+            definition: true,
+            frontmatter: false,
+            gfm_autolink_literal: false,
+            gfm_label_start_footnote: false,
+            gfm_footnote_definition: false,
+            gfm_strikethrough: false,
+            gfm_table: false,
+            gfm_task_list_item: false,
+            hard_break_escape: true,
+            hard_break_trailing: true,
+            heading_atx: true,
+            heading_setext: true,
+            html_flow: true,
+            html_text: true,
+            label_start_image: true,
+            label_start_link: true,
+            label_end: true,
+            list_item: true,
+            math_flow: false,
+            math_text: false,
+            mdx_esm: false,
+            mdx_expression_flow: false,
+            mdx_expression_text: false,
+            mdx_jsx_flow: false,
+            mdx_jsx_text: false,
+            thematic_break: true,
+        }
+    }
+}
+
+impl Constructs {
+    /// GFM.
+    ///
+    /// GFM stands for **GitHub flavored markdown**.
+    /// GFM extends `CommonMark` and adds support for autolink literals,
+    /// footnotes, strikethrough, tables, and tasklists.
+    ///
+    /// For more information, see the GFM specification:
+    /// <https://github.github.com/gfm/>.
+    pub fn gfm() -> Self {
+        Self {
+            gfm_autolink_literal: true,
+            gfm_footnote_definition: true,
+            gfm_label_start_footnote: true,
+            gfm_strikethrough: true,
+            gfm_table: true,
+            gfm_task_list_item: true,
+            ..Self::default()
+        }
+    }
+
+    /// MDX.
+    ///
+    /// This turns on `CommonMark`, turns off some conflicting constructs
+    /// (autolinks, code (indented), and HTML), and turns on MDX (ESM,
+    /// expressions, and JSX).
+    ///
+    /// For more information, see the MDX website:
+    /// <https://mdxjs.com>.
+    ///
+    /// > 👉 **Note**: to support ESM, you *must* pass
+    /// > [`mdx_esm_parse`][MdxEsmParse] in [`ParseOptions`][] too.
+    /// > Otherwise, ESM is treated as normal markdown.
+    /// >
+    /// > You *can* pass
+    /// > [`mdx_expression_parse`][MdxExpressionParse]
+    /// > to parse expressions according to a certain grammar (typically, a
+    /// > programming language).
+    /// > Otherwise, expressions are parsed with a basic algorithm that only
+    /// > cares about braces.
+    pub fn mdx() -> Self {
+        Self {
+            autolink: false,
+            code_indented: false,
+            html_flow: false,
+            html_text: false,
+            mdx_esm: true,
+            mdx_expression_flow: true,
+            mdx_expression_text: true,
+            mdx_jsx_flow: true,
+            mdx_jsx_text: true,
+            ..Self::default()
+        }
+    }
+}
+
+/// Configuration that describes how to compile to HTML.
+///
+/// You likely either want to turn on the dangerous options
+/// (`allow_dangerous_html`, `allow_dangerous_protocol`) when dealing with
+/// input you trust, or want to customize how GFM footnotes are compiled
+/// (typically because the input markdown is not in English).
+///
+/// ## Examples
+///
+/// ```
+/// use markdown::CompileOptions;
+/// # fn main() {
+///
+/// // Use the default trait to get safe defaults:
+/// let safe = CompileOptions::default();
+///
+/// // Live dangerously / trust the author:
+/// let danger = CompileOptions {
+///   allow_dangerous_html: true,
+///   allow_dangerous_protocol: true,
+///   ..CompileOptions::default()
+/// };
+///
+/// // In French:
+/// let enFrançais = CompileOptions {
+///   gfm_footnote_label: Some("Notes de bas de page".into()),
+///   gfm_footnote_back_label: Some("Arrière".into()),
+///   ..CompileOptions::default()
+/// };
+/// # }
+/// ```
+#[allow(clippy::struct_excessive_bools)]
+#[derive(Clone, Debug, Default)]
+pub struct CompileOptions {
+    /// Whether to allow (dangerous) HTML.
+    ///
+    /// The default is `false`, which still parses the HTML according to
+    /// `CommonMark` but shows the HTML as text instead of as elements.
+    ///
+    /// Pass `true` for trusted content to get actual HTML elements.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html, to_html_with_options, CompileOptions, Options};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `markdown-rs` is safe by default:
+    /// assert_eq!(
+    ///     to_html("Hi, <i>venus</i>!"),
+    ///     "<p>Hi, &lt;i&gt;venus&lt;/i&gt;!</p>"
+    /// );
+    ///
+    /// // Turn `allow_dangerous_html` on to allow potentially dangerous HTML:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "Hi, <i>venus</i>!",
+    ///         &Options {
+    ///             compile: CompileOptions {
+    ///               allow_dangerous_html: true,
+    ///               ..CompileOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<p>Hi, <i>venus</i>!</p>"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub allow_dangerous_html: bool,
+
+    /// Whether to allow dangerous protocols in links and images.
+    ///
+    /// The default is `false`, which drops URLs in links and images that use
+    /// dangerous protocols.
+    ///
+    /// Pass `true` for trusted content to support all protocols.
+    ///
+    /// URLs that have no protocol (which means it’s relative to the current
+    /// page, such as `./some/page.html`) and URLs that have a safe protocol
+    /// (for images: `http`, `https`; for links: `http`, `https`, `irc`,
+    /// `ircs`, `mailto`, `xmpp`), are safe.
+    /// All other URLs are dangerous and dropped.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html, to_html_with_options, CompileOptions, Options};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `markdown-rs` is safe by default:
+    /// assert_eq!(
+    ///     to_html("<javascript:alert(1)>"),
+    ///     "<p><a href=\"\">javascript:alert(1)</a></p>"
+    /// );
+    ///
+    /// // Turn `allow_dangerous_protocol` on to allow potentially dangerous protocols:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "<javascript:alert(1)>",
+    ///         &Options {
+    ///             compile: CompileOptions {
+    ///               allow_dangerous_protocol: true,
+    ///               ..CompileOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<p><a href=\"javascript:alert(1)\">javascript:alert(1)</a></p>"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub allow_dangerous_protocol: bool,
+
+    /// Default line ending to use when compiling to HTML, for line endings not
+    /// in `value`.
+    ///
+    /// Generally, `markdown-rs` copies line endings (`\r`, `\n`, `\r\n`) in
+    /// the markdown document over to the compiled HTML.
+    /// In some cases, such as `> a`, CommonMark requires that extra line
+    /// endings are added: `<blockquote>\n<p>a</p>\n</blockquote>`.
+    ///
+    /// To create that line ending, the document is checked for the first line
+    /// ending that is used.
+    /// If there is no line ending, `default_line_ending` is used.
+    /// If that isn’t configured, `\n` is used.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html, to_html_with_options, CompileOptions, LineEnding, Options};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `markdown-rs` uses `\n` by default:
+    /// assert_eq!(
+    ///     to_html("> a"),
+    ///     "<blockquote>\n<p>a</p>\n</blockquote>"
+    /// );
+    ///
+    /// // Define `default_line_ending` to configure the default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "> a",
+    ///         &Options {
+    ///             compile: CompileOptions {
+    ///               default_line_ending: LineEnding::CarriageReturnLineFeed,
+    ///               ..CompileOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<blockquote>\r\n<p>a</p>\r\n</blockquote>"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub default_line_ending: LineEnding,
+
+    /// Textual label to use for the footnotes section.
+    ///
+    /// The default value is `"Footnotes"`.
+    /// Change it when the markdown is not in English.
+    ///
+    /// This label is typically hidden visually (assuming a `sr-only` CSS class
+    /// is defined that does that), and thus affects screen readers only.
+    /// If you do have such a class, but want to show this section to everyone,
+    /// pass different attributes with the `gfm_footnote_label_attributes`
+    /// option.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `"Footnotes"` is used by default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options::gfm()
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    ///
+    /// // Pass `gfm_footnote_label` to use something else:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options {
+    ///             parse: ParseOptions::gfm(),
+    ///             compile: CompileOptions {
+    ///               gfm_footnote_label: Some("Notes de bas de page".into()),
+    ///               ..CompileOptions::gfm()
+    ///             }
+    ///         }
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Notes de bas de page</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub gfm_footnote_label: Option<String>,
+
+    /// HTML tag name to use for the footnote label element.
+    ///
+    /// The default value is `"h2"`.
+    /// Change it to match your document structure.
+    ///
+    /// This label is typically hidden visually (assuming a `sr-only` CSS class
+    /// is defined that does that), and thus affects screen readers only.
+    /// If you do have such a class, but want to show this section to everyone,
+    /// pass different attributes with the `gfm_footnote_label_attributes`
+    /// option.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `"h2"` is used by default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options::gfm()
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    ///
+    /// // Pass `gfm_footnote_label_tag_name` to use something else:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options {
+    ///             parse: ParseOptions::gfm(),
+    ///             compile: CompileOptions {
+    ///               gfm_footnote_label_tag_name: Some("h1".into()),
+    ///               ..CompileOptions::gfm()
+    ///             }
+    ///         }
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h1 id=\"footnote-label\" class=\"sr-only\">Footnotes</h1>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub gfm_footnote_label_tag_name: Option<String>,
+
+    /// Attributes to use on the footnote label.
+    ///
+    /// The default value is `"class=\"sr-only\""`.
+    /// Change it to show the label and add other attributes.
+    ///
+    /// This label is typically hidden visually (assuming a `sr-only` CSS class
+    /// is defined that does that), and thus affects screen readers only.
+    /// If you do have such a class, but want to show this section to everyone,
+    /// pass an empty string.
+    /// You can also add different attributes.
+    ///
+    /// > 👉 **Note**: `id="footnote-label"` is always added, because footnote
+    /// > calls use it with `aria-describedby` to provide an accessible label.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `"class=\"sr-only\""` is used by default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options::gfm()
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    ///
+    /// // Pass `gfm_footnote_label_attributes` to use something else:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options {
+    ///             parse: ParseOptions::gfm(),
+    ///             compile: CompileOptions {
+    ///               gfm_footnote_label_attributes: Some("class=\"footnote-heading\"".into()),
+    ///               ..CompileOptions::gfm()
+    ///             }
+    ///         }
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"footnote-heading\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub gfm_footnote_label_attributes: Option<String>,
+
+    /// Textual label to describe the backreference back to footnote calls.
+    ///
+    /// The default value is `"Back to content"`.
+    /// Change it when the markdown is not in English.
+    ///
+    /// This label is used in the `aria-label` attribute on each backreference
+    /// (the `↩` links).
+    /// It affects users of assistive technology.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `"Back to content"` is used by default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options::gfm()
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    ///
+    /// // Pass `gfm_footnote_back_label` to use something else:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options {
+    ///             parse: ParseOptions::gfm(),
+    ///             compile: CompileOptions {
+    ///               gfm_footnote_back_label: Some("Arrière".into()),
+    ///               ..CompileOptions::gfm()
+    ///             }
+    ///         }
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Arrière\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub gfm_footnote_back_label: Option<String>,
+
+    /// Prefix to use before the `id` attribute on footnotes to prevent them
+    /// from *clobbering*.
+    ///
+    /// The default is `"user-content-"`.
+    /// Pass `Some("".into())` for trusted markdown and when you are careful
+    /// with polyfilling.
+    /// You could pass a different prefix.
+    ///
+    /// DOM clobbering is this:
+    ///
+    /// ```html
+    /// <p id="x"></p>
+    /// <script>alert(x) // `x` now refers to the `p#x` DOM element</script>
+    /// ```
+    ///
+    /// The above example shows that elements are made available by browsers,
+    /// by their ID, on the `window` object.
+    /// This is a security risk because you might be expecting some other
+    /// variable at that place.
+    /// It can also break polyfills.
+    /// Using a prefix solves these problems.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `"user-content-"` is used by default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options::gfm()
+    ///     )?,
+    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    ///
+    /// // Pass `gfm_footnote_clobber_prefix` to use something else:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "[^a]\n\n[^a]: b",
+    ///         &Options {
+    ///             parse: ParseOptions::gfm(),
+    ///             compile: CompileOptions {
+    ///               gfm_footnote_clobber_prefix: Some("".into()),
+    ///               ..CompileOptions::gfm()
+    ///             }
+    ///         }
+    ///     )?,
+    ///     "<p><sup><a href=\"#fn-a\" id=\"fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"fn-a\">\n<p>b <a href=\"#fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub gfm_footnote_clobber_prefix: Option<String>,
+
+    /// Whether to support the GFM tagfilter.
+    ///
+    /// This option does nothing if `allow_dangerous_html` is not turned on.
+    /// The default is `false`, which does not apply the GFM tagfilter to HTML.
+    /// Pass `true` for output that is a bit closer to GitHub’s actual output.
+    ///
+    /// The tagfilter is kinda weird and kinda useless.
+    /// The tag filter is a naïve attempt at XSS protection.
+    /// You should use a proper HTML sanitizing algorithm instead.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // With `allow_dangerous_html`, `markdown-rs` passes HTML through untouched:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "<iframe>",
+    ///         &Options {
+    ///             parse: ParseOptions::gfm(),
+    ///             compile: CompileOptions {
+    ///               allow_dangerous_html: true,
+    ///               ..CompileOptions::default()
+    ///             }
+    ///         }
+    ///     )?,
+    ///     "<iframe>"
+    /// );
+    ///
+    /// // Pass `gfm_tagfilter: true` to make some of that safe:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "<iframe>",
+    ///         &Options {
+    ///             parse: ParseOptions::gfm(),
+    ///             compile: CompileOptions {
+    ///               allow_dangerous_html: true,
+    ///               gfm_tagfilter: true,
+    ///               ..CompileOptions::default()
+    ///             }
+    ///         }
+    ///     )?,
+    ///     "&lt;iframe>"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// ## References
+    ///
+    /// *   [*§ 6.1 Disallowed Raw HTML (extension)* in GFM](https://github.github.com/gfm/#disallowed-raw-html-extension-)
+    /// *   [`cmark-gfm#extensions/tagfilter.c`](https://github.com/github/cmark-gfm/blob/master/extensions/tagfilter.c)
+    pub gfm_tagfilter: bool,
+}
+
+impl CompileOptions {
+    /// GFM.
+    ///
+    /// GFM stands for **GitHub flavored markdown**.
+    /// On the compilation side, GFM turns on the GFM tag filter.
+    /// The tagfilter is useless, but it’s included here for consistency, and
+    /// this method exists for parity to parse options.
+    ///
+    /// For more information, see the GFM specification:
+    /// <https://github.github.com/gfm/>.
+    pub fn gfm() -> Self {
+        Self {
+            gfm_tagfilter: true,
+            ..Self::default()
+        }
+    }
+}
+
+/// Configuration that describes how to parse from markdown.
+///
+/// You can use this:
+///
+/// *   To control what markdown constructs are turned on and off
+/// *   To control some of those constructs
+/// *   To add support for certain programming languages when parsing MDX
+///
+/// In most cases, you will want to use the default trait or `gfm` method.
+///
+/// ## Examples
+///
+/// ```
+/// use markdown::ParseOptions;
+/// # fn main() {
+///
+/// // Use the default trait to parse markdown according to `CommonMark`:
+/// let commonmark = ParseOptions::default();
+///
+/// // Use the `gfm` method to parse markdown according to GFM:
+/// let gfm = ParseOptions::gfm();
+/// # }
+/// ```
+#[allow(clippy::struct_excessive_bools)]
+pub struct ParseOptions {
+    // Note: when adding fields, don’t forget to add them to `fmt::Debug` below.
+    /// Which constructs to enable and disable.
+    ///
+    /// The default is to follow `CommonMark`.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html, to_html_with_options, Constructs, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `markdown-rs` follows CommonMark by default:
+    /// assert_eq!(
+    ///     to_html("    indented code?"),
+    ///     "<pre><code>indented code?\n</code></pre>"
+    /// );
+    ///
+    /// // Pass `constructs` to choose what to enable and disable:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "    indented code?",
+    ///         &Options {
+    ///             parse: ParseOptions {
+    ///               constructs: Constructs {
+    ///                 code_indented: false,
+    ///                 ..Constructs::default()
+    ///               },
+    ///               ..ParseOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<p>indented code?</p>"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub constructs: Constructs,
+
+    /// Whether to support GFM strikethrough with a single tilde
+    ///
+    /// This option does nothing if `gfm_strikethrough` is not turned on in
+    /// `constructs`.
+    /// This option does not affect strikethrough with double tildes.
+    ///
+    /// The default is `true`, which follows how markdown on `github.com`
+    /// works, as strikethrough with single tildes is supported.
+    /// Pass `false`, to follow the GFM spec more strictly, by not allowing
+    /// strikethrough with single tildes.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, Constructs, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `markdown-rs` supports single tildes by default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "~a~",
+    ///         &Options {
+    ///             parse: ParseOptions {
+    ///               constructs: Constructs::gfm(),
+    ///               ..ParseOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<p><del>a</del></p>"
+    /// );
+    ///
+    /// // Pass `gfm_strikethrough_single_tilde: false` to turn that off:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "~a~",
+    ///         &Options {
+    ///             parse: ParseOptions {
+    ///               constructs: Constructs::gfm(),
+    ///               gfm_strikethrough_single_tilde: false,
+    ///               ..ParseOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<p>~a~</p>"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub gfm_strikethrough_single_tilde: bool,
+
+    /// Whether to support math (text) with a single dollar
+    ///
+    /// This option does nothing if `math_text` is not turned on in
+    /// `constructs`.
+    /// This option does not affect math (text) with two or more dollars.
+    ///
+    /// The default is `true`, which is more close to how code (text) and
+    /// Pandoc work, as it allows math with a single dollar to form.
+    /// However, single dollars can interfere with “normal” dollars in text.
+    /// Pass `false`, to only allow math (text) to form when two or more
+    /// dollars are used.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use markdown::{to_html_with_options, Constructs, Options, ParseOptions};
+    /// # fn main() -> Result<(), String> {
+    ///
+    /// // `markdown-rs` supports single dollars by default:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "$a$",
+    ///         &Options {
+    ///             parse: ParseOptions {
+    ///               constructs: Constructs {
+    ///                 math_text: true,
+    ///                 ..Constructs::default()
+    ///               },
+    ///               ..ParseOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<p><code class=\"language-math math-inline\">a</code></p>"
+    /// );
+    ///
+    /// // Pass `math_text_single_dollar: false` to turn that off:
+    /// assert_eq!(
+    ///     to_html_with_options(
+    ///         "$a$",
+    ///         &Options {
+    ///             parse: ParseOptions {
+    ///               constructs: Constructs {
+    ///                 math_text: true,
+    ///                 ..Constructs::default()
+    ///               },
+    ///               math_text_single_dollar: false,
+    ///               ..ParseOptions::default()
+    ///             },
+    ///             ..Options::default()
+    ///         }
+    ///     )?,
+    ///     "<p>$a$</p>"
+    /// );
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub math_text_single_dollar: bool,
+
+    /// Function to parse expressions with.
+    ///
+    /// This function can be used to add support for arbitrary programming
+    /// languages within expressions.
+    ///
+    /// It only makes sense to pass this when compiling to a syntax tree
+    /// with [`to_mdast()`][].
+    ///
+    /// For an example that adds support for JavaScript with SWC, see
+    /// `tests/test_utils/mod.rs`.
+    pub mdx_expression_parse: Option<Box<MdxExpressionParse>>,
+
+    /// Function to parse ESM with.
+    ///
+    /// This function can be used to add support for arbitrary programming
+    /// languages within ESM blocks, however, the keywords (`export`,
+    /// `import`) are currently hardcoded JavaScript-specific.
+    ///
+    /// > 👉 **Note**: please raise an issue if you’re interested in working on
+    /// > MDX that is aware of, say, Rust, or other programming languages.
+    ///
+    /// It only makes sense to pass this when compiling to a syntax tree
+    /// with [`to_mdast()`][].
+    ///
+    /// For an example that adds support for JavaScript with SWC, see
+    /// `tests/test_utils/mod.rs`.
+    pub mdx_esm_parse: Option<Box<MdxEsmParse>>,
+    // Note: when adding fields, don’t forget to add them to `fmt::Debug` below.
+}
+
+impl fmt::Debug for ParseOptions {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ParseOptions")
+            .field("constructs", &self.constructs)
+            .field(
+                "gfm_strikethrough_single_tilde",
+                &self.gfm_strikethrough_single_tilde,
+            )
+            .field("math_text_single_dollar", &self.math_text_single_dollar)
+            .field(
+                "mdx_expression_parse",
+                &self.mdx_expression_parse.as_ref().map(|_d| "[Function]"),
+            )
+            .field(
+                "mdx_esm_parse",
+                &self.mdx_esm_parse.as_ref().map(|_d| "[Function]"),
+            )
+            .finish()
+    }
+}
+
+impl Default for ParseOptions {
+    /// `CommonMark` defaults.
+    fn default() -> Self {
+        Self {
+            constructs: Constructs::default(),
+            gfm_strikethrough_single_tilde: true,
+            math_text_single_dollar: true,
+            mdx_expression_parse: None,
+            mdx_esm_parse: None,
+        }
+    }
+}
+
+impl ParseOptions {
+    /// GFM.
+    ///
+    /// GFM stands for GitHub flavored markdown.
+    /// GFM extends `CommonMark` and adds support for autolink literals,
+    /// footnotes, strikethrough, tables, and tasklists.
+    ///
+    /// For more information, see the GFM specification:
+    /// <https://github.github.com/gfm/>
+    pub fn gfm() -> Self {
+        Self {
+            constructs: Constructs::gfm(),
+            ..Self::default()
+        }
+    }
+
+    /// MDX.
+    ///
+    /// This turns on `CommonMark`, turns off some conflicting constructs
+    /// (autolinks, code (indented), and HTML), and turns on MDX (ESM,
+    /// expressions, and JSX).
+    ///
+    /// For more information, see the MDX website:
+    /// <https://mdxjs.com>.
+    ///
+    /// > 👉 **Note**: to support ESM, you *must* pass
+    /// > [`mdx_esm_parse`][MdxEsmParse] in [`ParseOptions`][] too.
+    /// > Otherwise, ESM is treated as normal markdown.
+    /// >
+    /// > You *can* pass
+    /// > [`mdx_expression_parse`][MdxExpressionParse]
+    /// > to parse expressions according to a certain grammar (typically, a
+    /// > programming language).
+    /// > Otherwise, expressions are parsed with a basic algorithm that only
+    /// > cares about braces.
+    pub fn mdx() -> Self {
+        Self {
+            constructs: Constructs::mdx(),
+            ..Self::default()
+        }
+    }
+}
+
+/// Configuration that describes how to parse from markdown and compile to
+/// HTML.
+///
+/// In most cases, you will want to use the default trait or `gfm` method.
+///
+/// ## Examples
+///
+/// ```
+/// use markdown::Options;
+/// # fn main() {
+///
+/// // Use the default trait to compile markdown to HTML according to `CommonMark`:
+/// let commonmark = Options::default();
+///
+/// // Use the `gfm` method to compile markdown to HTML according to GFM:
+/// let gfm = Options::gfm();
+/// # }
+/// ```
+#[allow(clippy::struct_excessive_bools)]
+#[derive(Debug, Default)]
+pub struct Options {
+    /// Configuration that describes how to parse from markdown.
+    pub parse: ParseOptions,
+    /// Configuration that describes how to compile to HTML.
+    pub compile: CompileOptions,
+}
+
+impl Options {
+    /// GFM.
+    ///
+    /// GFM stands for GitHub flavored markdown.
+    /// GFM extends `CommonMark` and adds support for autolink literals,
+    /// footnotes, strikethrough, tables, and tasklists.
+    /// On the compilation side, GFM turns on the GFM tag filter.
+    /// The tagfilter is useless, but it’s included here for consistency.
+    ///
+    /// For more information, see the GFM specification:
+    /// <https://github.github.com/gfm/>
+    pub fn gfm() -> Self {
+        Self {
+            parse: ParseOptions::gfm(),
+            compile: CompileOptions::gfm(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    extern crate std;
+    use super::*;
+    use crate::util::mdx::Signal;
+    use alloc::format;
+
+    #[test]
+    fn test_constructs() {
+        Constructs::default();
+        Constructs::gfm();
+        Constructs::mdx();
+
+        let constructs = Constructs::default();
+        assert!(constructs.attention, "should default to `CommonMark` (1)");
+        assert!(
+            !constructs.gfm_autolink_literal,
+            "should default to `CommonMark` (2)"
+        );
+        assert!(
+            !constructs.mdx_jsx_flow,
+            "should default to `CommonMark` (3)"
+        );
+        assert!(
+            !constructs.frontmatter,
+            "should default to `CommonMark` (4)"
+        );
+
+        let constructs = Constructs::gfm();
+        assert!(constructs.attention, "should support `gfm` shortcut (1)");
+        assert!(
+            constructs.gfm_autolink_literal,
+            "should support `gfm` shortcut (2)"
+        );
+        assert!(
+            !constructs.mdx_jsx_flow,
+            "should support `gfm` shortcut (3)"
+        );
+        assert!(!constructs.frontmatter, "should support `gfm` shortcut (4)");
+
+        let constructs = Constructs::mdx();
+        assert!(constructs.attention, "should support `gfm` shortcut (1)");
+        assert!(
+            !constructs.gfm_autolink_literal,
+            "should support `mdx` shortcut (2)"
+        );
+        assert!(constructs.mdx_jsx_flow, "should support `mdx` shortcut (3)");
+        assert!(!constructs.frontmatter, "should support `mdx` shortcut (4)");
+    }
+
+    #[test]
+    fn test_parse_options() {
+        ParseOptions::default();
+        ParseOptions::gfm();
+        ParseOptions::mdx();
+
+        let options = ParseOptions::default();
+        assert!(
+            options.constructs.attention,
+            "should default to `CommonMark` (1)"
+        );
+        assert!(
+            !options.constructs.gfm_autolink_literal,
+            "should default to `CommonMark` (2)"
+        );
+        assert!(
+            !options.constructs.mdx_jsx_flow,
+            "should default to `CommonMark` (3)"
+        );
+
+        let options = ParseOptions::gfm();
+        assert!(
+            options.constructs.attention,
+            "should support `gfm` shortcut (1)"
+        );
+        assert!(
+            options.constructs.gfm_autolink_literal,
+            "should support `gfm` shortcut (2)"
+        );
+        assert!(
+            !options.constructs.mdx_jsx_flow,
+            "should support `gfm` shortcut (3)"
+        );
+
+        let options = ParseOptions::mdx();
+        assert!(
+            options.constructs.attention,
+            "should support `mdx` shortcut (1)"
+        );
+        assert!(
+            !options.constructs.gfm_autolink_literal,
+            "should support `mdx` shortcut (2)"
+        );
+        assert!(
+            options.constructs.mdx_jsx_flow,
+            "should support `mdx` shortcut (3)"
+        );
+
+        assert_eq!(
+            format!("{:?}", ParseOptions::default()),
+            "ParseOptions { constructs: Constructs { attention: true, autolink: true, block_quote: true, character_escape: true, character_reference: true, code_indented: true, code_fenced: true, code_text: true, definition: true, frontmatter: false, gfm_autolink_literal: false, gfm_footnote_definition: false, gfm_label_start_footnote: false, gfm_strikethrough: false, gfm_table: false, gfm_task_list_item: false, hard_break_escape: true, hard_break_trailing: true, heading_atx: true, heading_setext: true, html_flow: true, html_text: true, label_start_image: true, label_start_link: true, label_end: true, list_item: true, math_flow: false, math_text: false, mdx_esm: false, mdx_expression_flow: false, mdx_expression_text: false, mdx_jsx_flow: false, mdx_jsx_text: false, thematic_break: true }, gfm_strikethrough_single_tilde: true, math_text_single_dollar: true, mdx_expression_parse: None, mdx_esm_parse: None }",
+            "should support `Debug` trait"
+        );
+        assert_eq!(
+            format!("{:?}", ParseOptions {
+                mdx_esm_parse: Some(Box::new(|_value| {
+                    Signal::Ok
+                })),
+                mdx_expression_parse: Some(Box::new(|_value, _kind| {
+                    Signal::Ok
+                })),
+                ..Default::default()
+            }),
+            "ParseOptions { constructs: Constructs { attention: true, autolink: true, block_quote: true, character_escape: true, character_reference: true, code_indented: true, code_fenced: true, code_text: true, definition: true, frontmatter: false, gfm_autolink_literal: false, gfm_footnote_definition: false, gfm_label_start_footnote: false, gfm_strikethrough: false, gfm_table: false, gfm_task_list_item: false, hard_break_escape: true, hard_break_trailing: true, heading_atx: true, heading_setext: true, html_flow: true, html_text: true, label_start_image: true, label_start_link: true, label_end: true, list_item: true, math_flow: false, math_text: false, mdx_esm: false, mdx_expression_flow: false, mdx_expression_text: false, mdx_jsx_flow: false, mdx_jsx_text: false, thematic_break: true }, gfm_strikethrough_single_tilde: true, math_text_single_dollar: true, mdx_expression_parse: Some(\"[Function]\"), mdx_esm_parse: Some(\"[Function]\") }",
+            "should support `Debug` trait on mdx functions"
+        );
+    }
+
+    #[test]
+    fn test_compile_options() {
+        CompileOptions::default();
+        CompileOptions::gfm();
+
+        let options = CompileOptions::default();
+        assert!(
+            !options.allow_dangerous_html,
+            "should default to safe `CommonMark` (1)"
+        );
+        assert!(
+            !options.gfm_tagfilter,
+            "should default to safe `CommonMark` (2)"
+        );
+
+        let options = CompileOptions::gfm();
+        assert!(
+            !options.allow_dangerous_html,
+            "should support safe `gfm` shortcut (1)"
+        );
+        assert!(
+            options.gfm_tagfilter,
+            "should support safe `gfm` shortcut (1)"
+        );
+    }
+
+    #[test]
+    fn test_options() {
+        Options::default();
+
+        let options = Options::default();
+        assert!(
+            options.parse.constructs.attention,
+            "should default to safe `CommonMark` (1)"
+        );
+        assert!(
+            !options.parse.constructs.gfm_autolink_literal,
+            "should default to safe `CommonMark` (2)"
+        );
+        assert!(
+            !options.parse.constructs.mdx_jsx_flow,
+            "should default to safe `CommonMark` (3)"
+        );
+        assert!(
+            !options.compile.allow_dangerous_html,
+            "should default to safe `CommonMark` (4)"
+        );
+
+        let options = Options::gfm();
+        assert!(
+            options.parse.constructs.attention,
+            "should support safe `gfm` shortcut (1)"
+        );
+        assert!(
+            options.parse.constructs.gfm_autolink_literal,
+            "should support safe `gfm` shortcut (2)"
+        );
+        assert!(
+            !options.parse.constructs.mdx_jsx_flow,
+            "should support safe `gfm` shortcut (3)"
+        );
+        assert!(
+            !options.compile.allow_dangerous_html,
+            "should support safe `gfm` shortcut (4)"
+        );
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index f655bbc..ab4c08e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -22,10 +22,9 @@
 )]
 
 extern crate alloc;
-
+mod configuration;
 mod construct;
 mod event;
-pub mod mdast; // To do: externalize?
 mod parser;
 mod resolve;
 mod state;
@@ -33,12 +32,10 @@ mod subtokenize;
 mod to_html;
 mod to_mdast;
 mod tokenizer;
-pub mod unist; // To do: externalize.
 mod util;
 
-use alloc::{boxed::Box, fmt, string::String};
-use mdast::Node;
-use parser::parse;
+pub mod mdast; // To do: externalize?
+pub mod unist; // To do: externalize.
 
 #[doc(hidden)]
 pub use util::identifier::{id_cont, id_start};
@@ -56,1240 +53,9 @@ pub use util::mdx::{
     ExpressionParse as MdxExpressionParse, Signal as MdxSignal,
 };
 
-/// Control which constructs are enabled.
-///
-/// Not all constructs can be configured.
-/// Notably, blank lines and paragraphs cannot be turned off.
-///
-/// ## Examples
-///
-/// ```
-/// use markdown::Constructs;
-/// # fn main() {
-///
-/// // Use the default trait to get `CommonMark` constructs:
-/// let commonmark = Constructs::default();
-///
-/// // To turn on all of GFM, use the `gfm` method:
-/// let gfm = Constructs::gfm();
-///
-/// // Or, mix and match:
-/// let custom = Constructs {
-///   math_flow: true,
-///   math_text: true,
-///   ..Constructs::gfm()
-/// };
-/// # }
-/// ```
-#[allow(clippy::struct_excessive_bools)]
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct Constructs {
-    /// Attention.
-    ///
-    /// ```markdown
-    /// > | a *b* c **d**.
-    ///       ^^^   ^^^^^
-    /// ```
-    pub attention: bool,
-    /// Autolink.
-    ///
-    /// ```markdown
-    /// > | a <https://example.com> b <user@example.org>.
-    ///       ^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^
-    /// ```
-    pub autolink: bool,
-    /// Block quote.
-    ///
-    /// ```markdown
-    /// > | > a
-    ///     ^^^
-    /// ```
-    pub block_quote: bool,
-    /// Character escape.
-    ///
-    /// ```markdown
-    /// > | a \* b
-    ///       ^^
-    /// ```
-    pub character_escape: bool,
-    /// Character reference.
-    ///
-    /// ```markdown
-    /// > | a &amp; b
-    ///       ^^^^^
-    /// ```
-    pub character_reference: bool,
-    /// Code (indented).
-    ///
-    /// ```markdown
-    /// > |     a
-    ///     ^^^^^
-    /// ```
-    pub code_indented: bool,
-    /// Code (fenced).
-    ///
-    /// ```markdown
-    /// > | ~~~js
-    ///     ^^^^^
-    /// > | console.log(1)
-    ///     ^^^^^^^^^^^^^^
-    /// > | ~~~
-    ///     ^^^
-    /// ```
-    pub code_fenced: bool,
-    /// Code (text).
-    ///
-    /// ```markdown
-    /// > | a `b` c
-    ///       ^^^
-    /// ```
-    pub code_text: bool,
-    /// Definition.
-    ///
-    /// ```markdown
-    /// > | [a]: b "c"
-    ///     ^^^^^^^^^^
-    /// ```
-    pub definition: bool,
-    /// Frontmatter.
-    ///
-    /// ````markdown
-    /// > | ---
-    ///     ^^^
-    /// > | title: Neptune
-    ///     ^^^^^^^^^^^^^^
-    /// > | ---
-    ///     ^^^
-    /// ````
-    pub frontmatter: bool,
-    /// GFM: autolink literal.
-    ///
-    /// ```markdown
-    /// > | https://example.com
-    ///     ^^^^^^^^^^^^^^^^^^^
-    /// ```
-    pub gfm_autolink_literal: bool,
-    /// GFM: footnote definition.
-    ///
-    /// ```markdown
-    /// > | [^a]: b
-    ///     ^^^^^^^
-    /// ```
-    pub gfm_footnote_definition: bool,
-    /// GFM: footnote label start.
-    ///
-    /// ```markdown
-    /// > | a[^b]
-    ///      ^^
-    /// ```
-    pub gfm_label_start_footnote: bool,
-    ///
-    /// ```markdown
-    /// > | a ~b~ c.
-    ///       ^^^
-    /// ```
-    pub gfm_strikethrough: bool,
-    /// GFM: table.
-    ///
-    /// ```markdown
-    /// > | | a |
-    ///     ^^^^^
-    /// > | | - |
-    ///     ^^^^^
-    /// > | | b |
-    ///     ^^^^^
-    /// ```
-    pub gfm_table: bool,
-    /// GFM: task list item.
-    ///
-    /// ```markdown
-    /// > | * [x] y.
-    ///       ^^^
-    /// ```
-    pub gfm_task_list_item: bool,
-    /// Hard break (escape).
-    ///
-    /// ```markdown
-    /// > | a\
-    ///      ^
-    ///   | b
-    /// ```
-    pub hard_break_escape: bool,
-    /// Hard break (trailing).
-    ///
-    /// ```markdown
-    /// > | a␠␠
-    ///      ^^
-    ///   | b
-    /// ```
-    pub hard_break_trailing: bool,
-    /// Heading (atx).
-    ///
-    /// ```markdown
-    /// > | # a
-    ///     ^^^
-    /// ```
-    pub heading_atx: bool,
-    /// Heading (setext).
-    ///
-    /// ```markdown
-    /// > | a
-    ///     ^^
-    /// > | ==
-    ///     ^^
-    /// ```
-    pub heading_setext: bool,
-    /// HTML (flow).
-    ///
-    /// ```markdown
-    /// > | <div>
-    ///     ^^^^^
-    /// ```
-    pub html_flow: bool,
-    /// HTML (text).
-    ///
-    /// ```markdown
-    /// > | a <b> c
-    ///       ^^^
-    /// ```
-    pub html_text: bool,
-    /// Label start (image).
-    ///
-    /// ```markdown
-    /// > | a ![b](c) d
-    ///       ^^
-    /// ```
-    pub label_start_image: bool,
-    /// Label start (link).
-    ///
-    /// ```markdown
-    /// > | a [b](c) d
-    ///       ^
-    /// ```
-    pub label_start_link: bool,
-    /// Label end.
-    ///
-    /// ```markdown
-    /// > | a [b](c) d
-    ///         ^^^^
-    /// ```
-    pub label_end: bool,
-    /// List items.
-    ///
-    /// ```markdown
-    /// > | * a
-    ///     ^^^
-    /// ```
-    pub list_item: bool,
-    /// Math (flow).
-    ///
-    /// ```markdown
-    /// > | $$
-    ///     ^^
-    /// > | \frac{1}{2}
-    ///     ^^^^^^^^^^^
-    /// > | $$
-    ///     ^^
-    /// ```
-    pub math_flow: bool,
-    /// Math (text).
-    ///
-    /// ```markdown
-    /// > | a $b$ c
-    ///       ^^^
-    /// ```
-    pub math_text: bool,
-    /// MDX: ESM.
-    ///
-    /// ```markdown
-    /// > | import a from 'b'
-    ///     ^^^^^^^^^^^^^^^^^
-    /// ```
-    ///
-    /// > 👉 **Note**: to support ESM, you *must* pass
-    /// > [`mdx_esm_parse`][MdxEsmParse] in [`ParseOptions`][] too.
-    /// > Otherwise, ESM is treated as normal markdown.
-    pub mdx_esm: bool,
-    /// MDX: expression (flow).
-    ///
-    /// ```markdown
-    /// > | {Math.PI}
-    ///     ^^^^^^^^^
-    /// ```
-    ///
-    /// > 👉 **Note**: You *can* pass
-    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
-    /// > too, to parse expressions according to a certain grammar (typically,
-    /// > a programming language).
-    /// > Otherwise, expressions are parsed with a basic algorithm that only
-    /// > cares about braces.
-    pub mdx_expression_flow: bool,
-    /// MDX: expression (text).
-    ///
-    /// ```markdown
-    /// > | a {Math.PI} c
-    ///       ^^^^^^^^^
-    /// ```
-    ///
-    /// > 👉 **Note**: You *can* pass
-    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
-    /// > too, to parse expressions according to a certain grammar (typically,
-    /// > a programming language).
-    /// > Otherwise, expressions are parsed with a basic algorithm that only
-    /// > cares about braces.
-    pub mdx_expression_text: bool,
-    /// MDX: JSX (flow).
-    ///
-    /// ```markdown
-    /// > | <Component />
-    ///     ^^^^^^^^^^^^^
-    /// ```
-    ///
-    /// > 👉 **Note**: You *must* pass `html_flow: false` to use this,
-    /// > as it’s preferred when on over `mdx_jsx_flow`.
-    ///
-    /// > 👉 **Note**: You *can* pass
-    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
-    /// > too, to parse expressions in JSX according to a certain grammar
-    /// > (typically, a programming language).
-    /// > Otherwise, expressions are parsed with a basic algorithm that only
-    /// > cares about braces.
-    pub mdx_jsx_flow: bool,
-    /// MDX: JSX (text).
-    ///
-    /// ```markdown
-    /// > | a <Component /> c
-    ///       ^^^^^^^^^^^^^
-    /// ```
-    ///
-    /// > 👉 **Note**: You *must* pass `html_text: false` to use this,
-    /// > as it’s preferred when on over `mdx_jsx_text`.
-    ///
-    /// > 👉 **Note**: You *can* pass
-    /// > [`mdx_expression_parse`][MdxExpressionParse] in [`ParseOptions`][]
-    /// > too, to parse expressions in JSX according to a certain grammar
-    /// > (typically, a programming language).
-    /// > Otherwise, expressions are parsed with a basic algorithm that only
-    /// > cares about braces.
-    pub mdx_jsx_text: bool,
-    /// Thematic break.
-    ///
-    /// ```markdown
-    /// > | ***
-    ///     ^^^
-    /// ```
-    pub thematic_break: bool,
-}
-
-// xxxxxxxxxxxxxxx
-impl Default for Constructs {
-    /// `CommonMark`.
-    ///
-    /// `CommonMark` is a relatively strong specification of how markdown
-    /// works.
-    /// Most markdown parsers try to follow it.
-    ///
-    /// For more information, see the `CommonMark` specification:
-    /// <https://spec.commonmark.org>.
-    fn default() -> Self {
-        Self {
-            attention: true,
-            autolink: true,
-            block_quote: true,
-            character_escape: true,
-            character_reference: true,
-            code_indented: true,
-            code_fenced: true,
-            code_text: true,
-            definition: true,
-            frontmatter: false,
-            gfm_autolink_literal: false,
-            gfm_label_start_footnote: false,
-            gfm_footnote_definition: false,
-            gfm_strikethrough: false,
-            gfm_table: false,
-            gfm_task_list_item: false,
-            hard_break_escape: true,
-            hard_break_trailing: true,
-            heading_atx: true,
-            heading_setext: true,
-            html_flow: true,
-            html_text: true,
-            label_start_image: true,
-            label_start_link: true,
-            label_end: true,
-            list_item: true,
-            math_flow: false,
-            math_text: false,
-            mdx_esm: false,
-            mdx_expression_flow: false,
-            mdx_expression_text: false,
-            mdx_jsx_flow: false,
-            mdx_jsx_text: false,
-            thematic_break: true,
-        }
-    }
-}
-
-impl Constructs {
-    /// GFM.
-    ///
-    /// GFM stands for **GitHub flavored markdown**.
-    /// GFM extends `CommonMark` and adds support for autolink literals,
-    /// footnotes, strikethrough, tables, and tasklists.
-    ///
-    /// For more information, see the GFM specification:
-    /// <https://github.github.com/gfm/>.
-    // xxxxxxxxxxxxxxx
-    pub fn gfm() -> Self {
-        Self {
-            gfm_autolink_literal: true,
-            gfm_footnote_definition: true,
-            gfm_label_start_footnote: true,
-            gfm_strikethrough: true,
-            gfm_table: true,
-            gfm_task_list_item: true,
-            ..Self::default()
-        }
-    }
-
-    /// MDX.
-    ///
-    /// This turns on `CommonMark`, turns off some conflicting constructs
-    /// (autolinks, code (indented), and HTML), and turns on MDX (ESM,
-    /// expressions, and JSX).
-    ///
-    /// For more information, see the MDX website:
-    /// <https://mdxjs.com>.
-    ///
-    /// > 👉 **Note**: to support ESM, you *must* pass
-    /// > [`mdx_esm_parse`][MdxEsmParse] in [`ParseOptions`][] too.
-    /// > Otherwise, ESM is treated as normal markdown.
-    /// >
-    /// > You *can* pass
-    /// > [`mdx_expression_parse`][MdxExpressionParse]
-    /// > to parse expressions according to a certain grammar (typically, a
-    /// > programming language).
-    /// > Otherwise, expressions are parsed with a basic algorithm that only
-    /// > cares about braces.
-    // xxxxxxxxxxxxxxx
-    pub fn mdx() -> Self {
-        Self {
-            autolink: false,
-            code_indented: false,
-            html_flow: false,
-            html_text: false,
-            mdx_esm: true,
-            mdx_expression_flow: true,
-            mdx_expression_text: true,
-            mdx_jsx_flow: true,
-            mdx_jsx_text: true,
-            ..Self::default()
-        }
-    }
-}
-
-/// Configuration that describes how to compile to HTML.
-///
-/// You likely either want to turn on the dangerous options
-/// (`allow_dangerous_html`, `allow_dangerous_protocol`) when dealing with
-/// input you trust, or want to customize how GFM footnotes are compiled
-/// (typically because the input markdown is not in English).
-///
-/// ## Examples
-///
-/// ```
-/// use markdown::CompileOptions;
-/// # fn main() {
-///
-/// // Use the default trait to get safe defaults:
-/// let safe = CompileOptions::default();
-///
-/// // Live dangerously / trust the author:
-/// let danger = CompileOptions {
-///   allow_dangerous_html: true,
-///   allow_dangerous_protocol: true,
-///   ..CompileOptions::default()
-/// };
-///
-/// // In French:
-/// let enFrançais = CompileOptions {
-///   gfm_footnote_label: Some("Notes de bas de page".into()),
-///   gfm_footnote_back_label: Some("Arrière".into()),
-///   ..CompileOptions::default()
-/// };
-/// # }
-/// ```
-#[allow(clippy::struct_excessive_bools)]
-#[derive(Clone, Debug, Default)]
-pub struct CompileOptions {
-    /// Whether to allow (dangerous) HTML.
-    ///
-    /// The default is `false`, which still parses the HTML according to
-    /// `CommonMark` but shows the HTML as text instead of as elements.
-    ///
-    /// Pass `true` for trusted content to get actual HTML elements.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html, to_html_with_options, CompileOptions, Options};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `markdown-rs` is safe by default:
-    /// assert_eq!(
-    ///     to_html("Hi, <i>venus</i>!"),
-    ///     "<p>Hi, &lt;i&gt;venus&lt;/i&gt;!</p>"
-    /// );
-    ///
-    /// // Turn `allow_dangerous_html` on to allow potentially dangerous HTML:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "Hi, <i>venus</i>!",
-    ///         &Options {
-    ///             compile: CompileOptions {
-    ///               allow_dangerous_html: true,
-    ///               ..CompileOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<p>Hi, <i>venus</i>!</p>"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub allow_dangerous_html: bool,
-
-    /// Whether to allow dangerous protocols in links and images.
-    ///
-    /// The default is `false`, which drops URLs in links and images that use
-    /// dangerous protocols.
-    ///
-    /// Pass `true` for trusted content to support all protocols.
-    ///
-    /// URLs that have no protocol (which means it’s relative to the current
-    /// page, such as `./some/page.html`) and URLs that have a safe protocol
-    /// (for images: `http`, `https`; for links: `http`, `https`, `irc`,
-    /// `ircs`, `mailto`, `xmpp`), are safe.
-    /// All other URLs are dangerous and dropped.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html, to_html_with_options, CompileOptions, Options};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `markdown-rs` is safe by default:
-    /// assert_eq!(
-    ///     to_html("<javascript:alert(1)>"),
-    ///     "<p><a href=\"\">javascript:alert(1)</a></p>"
-    /// );
-    ///
-    /// // Turn `allow_dangerous_protocol` on to allow potentially dangerous protocols:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "<javascript:alert(1)>",
-    ///         &Options {
-    ///             compile: CompileOptions {
-    ///               allow_dangerous_protocol: true,
-    ///               ..CompileOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<p><a href=\"javascript:alert(1)\">javascript:alert(1)</a></p>"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub allow_dangerous_protocol: bool,
-
-    /// Default line ending to use when compiling to HTML, for line endings not
-    /// in `value`.
-    ///
-    /// Generally, `markdown-rs` copies line endings (`\r`, `\n`, `\r\n`) in
-    /// the markdown document over to the compiled HTML.
-    /// In some cases, such as `> a`, CommonMark requires that extra line
-    /// endings are added: `<blockquote>\n<p>a</p>\n</blockquote>`.
-    ///
-    /// To create that line ending, the document is checked for the first line
-    /// ending that is used.
-    /// If there is no line ending, `default_line_ending` is used.
-    /// If that isn’t configured, `\n` is used.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html, to_html_with_options, CompileOptions, LineEnding, Options};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `markdown-rs` uses `\n` by default:
-    /// assert_eq!(
-    ///     to_html("> a"),
-    ///     "<blockquote>\n<p>a</p>\n</blockquote>"
-    /// );
-    ///
-    /// // Define `default_line_ending` to configure the default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "> a",
-    ///         &Options {
-    ///             compile: CompileOptions {
-    ///               default_line_ending: LineEnding::CarriageReturnLineFeed,
-    ///               ..CompileOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<blockquote>\r\n<p>a</p>\r\n</blockquote>"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub default_line_ending: LineEnding,
-
-    /// Textual label to use for the footnotes section.
-    ///
-    /// The default value is `"Footnotes"`.
-    /// Change it when the markdown is not in English.
-    ///
-    /// This label is typically hidden visually (assuming a `sr-only` CSS class
-    /// is defined that does that), and thus affects screen readers only.
-    /// If you do have such a class, but want to show this section to everyone,
-    /// pass different attributes with the `gfm_footnote_label_attributes`
-    /// option.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `"Footnotes"` is used by default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options::gfm()
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    ///
-    /// // Pass `gfm_footnote_label` to use something else:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options {
-    ///             parse: ParseOptions::gfm(),
-    ///             compile: CompileOptions {
-    ///               gfm_footnote_label: Some("Notes de bas de page".into()),
-    ///               ..CompileOptions::gfm()
-    ///             }
-    ///         }
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Notes de bas de page</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub gfm_footnote_label: Option<String>,
-
-    /// HTML tag name to use for the footnote label element.
-    ///
-    /// The default value is `"h2"`.
-    /// Change it to match your document structure.
-    ///
-    /// This label is typically hidden visually (assuming a `sr-only` CSS class
-    /// is defined that does that), and thus affects screen readers only.
-    /// If you do have such a class, but want to show this section to everyone,
-    /// pass different attributes with the `gfm_footnote_label_attributes`
-    /// option.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `"h2"` is used by default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options::gfm()
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    ///
-    /// // Pass `gfm_footnote_label_tag_name` to use something else:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options {
-    ///             parse: ParseOptions::gfm(),
-    ///             compile: CompileOptions {
-    ///               gfm_footnote_label_tag_name: Some("h1".into()),
-    ///               ..CompileOptions::gfm()
-    ///             }
-    ///         }
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h1 id=\"footnote-label\" class=\"sr-only\">Footnotes</h1>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub gfm_footnote_label_tag_name: Option<String>,
-
-    /// Attributes to use on the footnote label.
-    ///
-    /// The default value is `"class=\"sr-only\""`.
-    /// Change it to show the label and add other attributes.
-    ///
-    /// This label is typically hidden visually (assuming a `sr-only` CSS class
-    /// is defined that does that), and thus affects screen readers only.
-    /// If you do have such a class, but want to show this section to everyone,
-    /// pass an empty string.
-    /// You can also add different attributes.
-    ///
-    /// > 👉 **Note**: `id="footnote-label"` is always added, because footnote
-    /// > calls use it with `aria-describedby` to provide an accessible label.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `"class=\"sr-only\""` is used by default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options::gfm()
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    ///
-    /// // Pass `gfm_footnote_label_attributes` to use something else:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options {
-    ///             parse: ParseOptions::gfm(),
-    ///             compile: CompileOptions {
-    ///               gfm_footnote_label_attributes: Some("class=\"footnote-heading\"".into()),
-    ///               ..CompileOptions::gfm()
-    ///             }
-    ///         }
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"footnote-heading\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub gfm_footnote_label_attributes: Option<String>,
-
-    /// Textual label to describe the backreference back to footnote calls.
-    ///
-    /// The default value is `"Back to content"`.
-    /// Change it when the markdown is not in English.
-    ///
-    /// This label is used in the `aria-label` attribute on each backreference
-    /// (the `↩` links).
-    /// It affects users of assistive technology.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `"Back to content"` is used by default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options::gfm()
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    ///
-    /// // Pass `gfm_footnote_back_label` to use something else:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options {
-    ///             parse: ParseOptions::gfm(),
-    ///             compile: CompileOptions {
-    ///               gfm_footnote_back_label: Some("Arrière".into()),
-    ///               ..CompileOptions::gfm()
-    ///             }
-    ///         }
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Arrière\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub gfm_footnote_back_label: Option<String>,
-
-    /// Prefix to use before the `id` attribute on footnotes to prevent them
-    /// from *clobbering*.
-    ///
-    /// The default is `"user-content-"`.
-    /// Pass `Some("".into())` for trusted markdown and when you are careful
-    /// with polyfilling.
-    /// You could pass a different prefix.
-    ///
-    /// DOM clobbering is this:
-    ///
-    /// ```html
-    /// <p id="x"></p>
-    /// <script>alert(x) // `x` now refers to the `p#x` DOM element</script>
-    /// ```
-    ///
-    /// The above example shows that elements are made available by browsers,
-    /// by their ID, on the `window` object.
-    /// This is a security risk because you might be expecting some other
-    /// variable at that place.
-    /// It can also break polyfills.
-    /// Using a prefix solves these problems.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `"user-content-"` is used by default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options::gfm()
-    ///     )?,
-    ///     "<p><sup><a href=\"#user-content-fn-a\" id=\"user-content-fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"user-content-fn-a\">\n<p>b <a href=\"#user-content-fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    ///
-    /// // Pass `gfm_footnote_clobber_prefix` to use something else:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "[^a]\n\n[^a]: b",
-    ///         &Options {
-    ///             parse: ParseOptions::gfm(),
-    ///             compile: CompileOptions {
-    ///               gfm_footnote_clobber_prefix: Some("".into()),
-    ///               ..CompileOptions::gfm()
-    ///             }
-    ///         }
-    ///     )?,
-    ///     "<p><sup><a href=\"#fn-a\" id=\"fnref-a\" data-footnote-ref=\"\" aria-describedby=\"footnote-label\">1</a></sup></p>\n<section data-footnotes=\"\" class=\"footnotes\"><h2 id=\"footnote-label\" class=\"sr-only\">Footnotes</h2>\n<ol>\n<li id=\"fn-a\">\n<p>b <a href=\"#fnref-a\" data-footnote-backref=\"\" aria-label=\"Back to content\" class=\"data-footnote-backref\">↩</a></p>\n</li>\n</ol>\n</section>\n"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub gfm_footnote_clobber_prefix: Option<String>,
+pub use configuration::{CompileOptions, Constructs, Options, ParseOptions};
 
-    /// Whether to support the GFM tagfilter.
-    ///
-    /// This option does nothing if `allow_dangerous_html` is not turned on.
-    /// The default is `false`, which does not apply the GFM tagfilter to HTML.
-    /// Pass `true` for output that is a bit closer to GitHub’s actual output.
-    ///
-    /// The tagfilter is kinda weird and kinda useless.
-    /// The tag filter is a naïve attempt at XSS protection.
-    /// You should use a proper HTML sanitizing algorithm instead.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, CompileOptions, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // With `allow_dangerous_html`, `markdown-rs` passes HTML through untouched:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "<iframe>",
-    ///         &Options {
-    ///             parse: ParseOptions::gfm(),
-    ///             compile: CompileOptions {
-    ///               allow_dangerous_html: true,
-    ///               ..CompileOptions::default()
-    ///             }
-    ///         }
-    ///     )?,
-    ///     "<iframe>"
-    /// );
-    ///
-    /// // Pass `gfm_tagfilter: true` to make some of that safe:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "<iframe>",
-    ///         &Options {
-    ///             parse: ParseOptions::gfm(),
-    ///             compile: CompileOptions {
-    ///               allow_dangerous_html: true,
-    ///               gfm_tagfilter: true,
-    ///               ..CompileOptions::default()
-    ///             }
-    ///         }
-    ///     )?,
-    ///     "&lt;iframe>"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    ///
-    /// ## References
-    ///
-    /// *   [*§ 6.1 Disallowed Raw HTML (extension)* in GFM](https://github.github.com/gfm/#disallowed-raw-html-extension-)
-    /// *   [`cmark-gfm#extensions/tagfilter.c`](https://github.com/github/cmark-gfm/blob/master/extensions/tagfilter.c)
-    pub gfm_tagfilter: bool,
-}
-
-// xxxxxxxxxxxxxxx
-impl CompileOptions {
-    /// GFM.
-    ///
-    /// GFM stands for **GitHub flavored markdown**.
-    /// On the compilation side, GFM turns on the GFM tag filter.
-    /// The tagfilter is useless, but it’s included here for consistency, and
-    /// this method exists for parity to parse options.
-    ///
-    /// For more information, see the GFM specification:
-    /// <https://github.github.com/gfm/>.
-    pub fn gfm() -> Self {
-        Self {
-            gfm_tagfilter: true,
-            ..Self::default()
-        }
-    }
-}
-
-/// Configuration that describes how to parse from markdown.
-///
-/// You can use this:
-///
-/// *   To control what markdown constructs are turned on and off
-/// *   To control some of those constructs
-/// *   To add support for certain programming languages when parsing MDX
-///
-/// In most cases, you will want to use the default trait or `gfm` method.
-///
-/// ## Examples
-///
-/// ```
-/// use markdown::ParseOptions;
-/// # fn main() {
-///
-/// // Use the default trait to parse markdown according to `CommonMark`:
-/// let commonmark = ParseOptions::default();
-///
-/// // Use the `gfm` method to parse markdown according to GFM:
-/// let gfm = ParseOptions::gfm();
-/// # }
-/// ```
-#[allow(clippy::struct_excessive_bools)]
-pub struct ParseOptions {
-    // Note: when adding fields, don’t forget to add them to `fmt::Debug` below.
-    /// Which constructs to enable and disable.
-    ///
-    /// The default is to follow `CommonMark`.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html, to_html_with_options, Constructs, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `markdown-rs` follows CommonMark by default:
-    /// assert_eq!(
-    ///     to_html("    indented code?"),
-    ///     "<pre><code>indented code?\n</code></pre>"
-    /// );
-    ///
-    /// // Pass `constructs` to choose what to enable and disable:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "    indented code?",
-    ///         &Options {
-    ///             parse: ParseOptions {
-    ///               constructs: Constructs {
-    ///                 code_indented: false,
-    ///                 ..Constructs::default()
-    ///               },
-    ///               ..ParseOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<p>indented code?</p>"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub constructs: Constructs,
-
-    /// Whether to support GFM strikethrough with a single tilde
-    ///
-    /// This option does nothing if `gfm_strikethrough` is not turned on in
-    /// `constructs`.
-    /// This option does not affect strikethrough with double tildes.
-    ///
-    /// The default is `true`, which follows how markdown on `github.com`
-    /// works, as strikethrough with single tildes is supported.
-    /// Pass `false`, to follow the GFM spec more strictly, by not allowing
-    /// strikethrough with single tildes.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, Constructs, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `markdown-rs` supports single tildes by default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "~a~",
-    ///         &Options {
-    ///             parse: ParseOptions {
-    ///               constructs: Constructs::gfm(),
-    ///               ..ParseOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<p><del>a</del></p>"
-    /// );
-    ///
-    /// // Pass `gfm_strikethrough_single_tilde: false` to turn that off:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "~a~",
-    ///         &Options {
-    ///             parse: ParseOptions {
-    ///               constructs: Constructs::gfm(),
-    ///               gfm_strikethrough_single_tilde: false,
-    ///               ..ParseOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<p>~a~</p>"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub gfm_strikethrough_single_tilde: bool,
-
-    /// Whether to support math (text) with a single dollar
-    ///
-    /// This option does nothing if `math_text` is not turned on in
-    /// `constructs`.
-    /// This option does not affect math (text) with two or more dollars.
-    ///
-    /// The default is `true`, which is more close to how code (text) and
-    /// Pandoc work, as it allows math with a single dollar to form.
-    /// However, single dollars can interfere with “normal” dollars in text.
-    /// Pass `false`, to only allow math (text) to form when two or more
-    /// dollars are used.
-    ///
-    /// ## Examples
-    ///
-    /// ```
-    /// use markdown::{to_html_with_options, Constructs, Options, ParseOptions};
-    /// # fn main() -> Result<(), String> {
-    ///
-    /// // `markdown-rs` supports single dollars by default:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "$a$",
-    ///         &Options {
-    ///             parse: ParseOptions {
-    ///               constructs: Constructs {
-    ///                 math_text: true,
-    ///                 ..Constructs::default()
-    ///               },
-    ///               ..ParseOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<p><code class=\"language-math math-inline\">a</code></p>"
-    /// );
-    ///
-    /// // Pass `math_text_single_dollar: false` to turn that off:
-    /// assert_eq!(
-    ///     to_html_with_options(
-    ///         "$a$",
-    ///         &Options {
-    ///             parse: ParseOptions {
-    ///               constructs: Constructs {
-    ///                 math_text: true,
-    ///                 ..Constructs::default()
-    ///               },
-    ///               math_text_single_dollar: false,
-    ///               ..ParseOptions::default()
-    ///             },
-    ///             ..Options::default()
-    ///         }
-    ///     )?,
-    ///     "<p>$a$</p>"
-    /// );
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub math_text_single_dollar: bool,
-
-    /// Function to parse expressions with.
-    ///
-    /// This function can be used to add support for arbitrary programming
-    /// languages within expressions.
-    ///
-    /// It only makes sense to pass this when compiling to a syntax tree
-    /// with [`to_mdast()`][].
-    ///
-    /// For an example that adds support for JavaScript with SWC, see
-    /// `tests/test_utils/mod.rs`.
-    pub mdx_expression_parse: Option<Box<MdxExpressionParse>>,
-
-    /// Function to parse ESM with.
-    ///
-    /// This function can be used to add support for arbitrary programming
-    /// languages within ESM blocks, however, the keywords (`export`,
-    /// `import`) are currently hardcoded JavaScript-specific.
-    ///
-    /// > 👉 **Note**: please raise an issue if you’re interested in working on
-    /// > MDX that is aware of, say, Rust, or other programming languages.
-    ///
-    /// It only makes sense to pass this when compiling to a syntax tree
-    /// with [`to_mdast()`][].
-    ///
-    /// For an example that adds support for JavaScript with SWC, see
-    /// `tests/test_utils/mod.rs`.
-    pub mdx_esm_parse: Option<Box<MdxEsmParse>>,
-    // Note: when adding fields, don’t forget to add them to `fmt::Debug` below.
-}
-
-impl fmt::Debug for ParseOptions {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("ParseOptions")
-            .field("constructs", &self.constructs)
-            .field(
-                "gfm_strikethrough_single_tilde",
-                &self.gfm_strikethrough_single_tilde,
-            )
-            .field("math_text_single_dollar", &self.math_text_single_dollar)
-            .field(
-                "mdx_expression_parse",
-                &self.mdx_expression_parse.as_ref().map(|_d| "[Function]"),
-            )
-            .field(
-                "mdx_esm_parse",
-                &self.mdx_esm_parse.as_ref().map(|_d| "[Function]"),
-            )
-            .finish()
-    }
-}
-
-impl Default for ParseOptions {
-    /// `CommonMark` defaults.
-    fn default() -> Self {
-        Self {
-            constructs: Constructs::default(),
-            gfm_strikethrough_single_tilde: true,
-            math_text_single_dollar: true,
-            mdx_expression_parse: None,
-            mdx_esm_parse: None,
-        }
-    }
-}
-
-impl ParseOptions {
-    /// GFM.
-    ///
-    /// GFM stands for GitHub flavored markdown.
-    /// GFM extends `CommonMark` and adds support for autolink literals,
-    /// footnotes, strikethrough, tables, and tasklists.
-    ///
-    /// For more information, see the GFM specification:
-    /// <https://github.github.com/gfm/>
-    pub fn gfm() -> Self {
-        Self {
-            constructs: Constructs::gfm(),
-            ..Self::default()
-        }
-    }
-
-    /// MDX.
-    ///
-    /// This turns on `CommonMark`, turns off some conflicting constructs
-    /// (autolinks, code (indented), and HTML), and turns on MDX (ESM,
-    /// expressions, and JSX).
-    ///
-    /// For more information, see the MDX website:
-    /// <https://mdxjs.com>.
-    ///
-    /// > 👉 **Note**: to support ESM, you *must* pass
-    /// > [`mdx_esm_parse`][MdxEsmParse] in [`ParseOptions`][] too.
-    /// > Otherwise, ESM is treated as normal markdown.
-    /// >
-    /// > You *can* pass
-    /// > [`mdx_expression_parse`][MdxExpressionParse]
-    /// > to parse expressions according to a certain grammar (typically, a
-    /// > programming language).
-    /// > Otherwise, expressions are parsed with a basic algorithm that only
-    /// > cares about braces.
-    // xxxxxxxxxxxxxxx
-    pub fn mdx() -> Self {
-        Self {
-            constructs: Constructs::mdx(),
-            ..Self::default()
-        }
-    }
-}
-
-/// Configuration that describes how to parse from markdown and compile to
-/// HTML.
-///
-/// In most cases, you will want to use the default trait or `gfm` method.
-///
-/// ## Examples
-///
-/// ```
-/// use markdown::Options;
-/// # fn main() {
-///
-/// // Use the default trait to compile markdown to HTML according to `CommonMark`:
-/// let commonmark = Options::default();
-///
-/// // Use the `gfm` method to compile markdown to HTML according to GFM:
-/// let gfm = Options::gfm();
-/// # }
-/// ```
-#[allow(clippy::struct_excessive_bools)]
-#[derive(Debug, Default)]
-pub struct Options {
-    /// Configuration that describes how to parse from markdown.
-    pub parse: ParseOptions,
-    /// Configuration that describes how to compile to HTML.
-    pub compile: CompileOptions,
-}
-
-impl Options {
-    /// GFM.
-    ///
-    /// GFM stands for GitHub flavored markdown.
-    /// GFM extends `CommonMark` and adds support for autolink literals,
-    /// footnotes, strikethrough, tables, and tasklists.
-    /// On the compilation side, GFM turns on the GFM tag filter.
-    /// The tagfilter is useless, but it’s included here for consistency.
-    ///
-    /// For more information, see the GFM specification:
-    /// <https://github.github.com/gfm/>
-    pub fn gfm() -> Self {
-        Self {
-            parse: ParseOptions::gfm(),
-            compile: CompileOptions::gfm(),
-        }
-    }
-}
+use alloc::string::String;
 
 /// Turn markdown into HTML.
 ///
@@ -1304,7 +70,6 @@ impl Options {
 ///
 /// assert_eq!(to_html("# Hello, world!"), "<h1>Hello, world!</h1>");
 /// ```
-// xxxxxxxxxxxxxxx
 pub fn to_html(value: &str) -> String {
     to_html_with_options(value, &Options::default()).unwrap()
 }
@@ -1345,7 +110,7 @@ pub fn to_html(value: &str) -> String {
 /// # }
 /// ```
 pub fn to_html_with_options(value: &str, options: &Options) -> Result<String, String> {
-    let (events, parse_state) = parse(value, &options.parse)?;
+    let (events, parse_state) = parser::parse(value, &options.parse)?;
     Ok(to_html::compile(
         &events,
         parse_state.bytes,
@@ -1376,8 +141,8 @@ pub fn to_html_with_options(value: &str, options: &Options) -> Result<String, St
 /// # Ok(())
 /// # }
 /// ```
-pub fn to_mdast(value: &str, options: &ParseOptions) -> Result<Node, String> {
-    let (events, parse_state) = parse(value, options)?;
+pub fn to_mdast(value: &str, options: &ParseOptions) -> Result<mdast::Node, String> {
+    let (events, parse_state) = parser::parse(value, options)?;
     let node = to_mdast::compile(&events, parse_state.bytes)?;
     Ok(node)
 }
@@ -1386,185 +151,6 @@ pub fn to_mdast(value: &str, options: &ParseOptions) -> Result<Node, String> {
 mod tests {
     extern crate std;
     use super::*;
-    use alloc::format;
-
-    #[test]
-    fn test_constructs() {
-        Constructs::default();
-        Constructs::gfm();
-        Constructs::mdx();
-
-        let constructs = Constructs::default();
-        assert!(constructs.attention, "should default to `CommonMark` (1)");
-        assert!(
-            !constructs.gfm_autolink_literal,
-            "should default to `CommonMark` (2)"
-        );
-        assert!(
-            !constructs.mdx_jsx_flow,
-            "should default to `CommonMark` (3)"
-        );
-        assert!(
-            !constructs.frontmatter,
-            "should default to `CommonMark` (4)"
-        );
-
-        let constructs = Constructs::gfm();
-        assert!(constructs.attention, "should support `gfm` shortcut (1)");
-        assert!(
-            constructs.gfm_autolink_literal,
-            "should support `gfm` shortcut (2)"
-        );
-        assert!(
-            !constructs.mdx_jsx_flow,
-            "should support `gfm` shortcut (3)"
-        );
-        assert!(!constructs.frontmatter, "should support `gfm` shortcut (4)");
-
-        let constructs = Constructs::mdx();
-        assert!(constructs.attention, "should support `gfm` shortcut (1)");
-        assert!(
-            !constructs.gfm_autolink_literal,
-            "should support `mdx` shortcut (2)"
-        );
-        assert!(constructs.mdx_jsx_flow, "should support `mdx` shortcut (3)");
-        assert!(!constructs.frontmatter, "should support `mdx` shortcut (4)");
-    }
-
-    #[test]
-    fn test_parse_options() {
-        ParseOptions::default();
-        ParseOptions::gfm();
-        ParseOptions::mdx();
-
-        let options = ParseOptions::default();
-        assert!(
-            options.constructs.attention,
-            "should default to `CommonMark` (1)"
-        );
-        assert!(
-            !options.constructs.gfm_autolink_literal,
-            "should default to `CommonMark` (2)"
-        );
-        assert!(
-            !options.constructs.mdx_jsx_flow,
-            "should default to `CommonMark` (3)"
-        );
-
-        let options = ParseOptions::gfm();
-        assert!(
-            options.constructs.attention,
-            "should support `gfm` shortcut (1)"
-        );
-        assert!(
-            options.constructs.gfm_autolink_literal,
-            "should support `gfm` shortcut (2)"
-        );
-        assert!(
-            !options.constructs.mdx_jsx_flow,
-            "should support `gfm` shortcut (3)"
-        );
-
-        let options = ParseOptions::mdx();
-        assert!(
-            options.constructs.attention,
-            "should support `mdx` shortcut (1)"
-        );
-        assert!(
-            !options.constructs.gfm_autolink_literal,
-            "should support `mdx` shortcut (2)"
-        );
-        assert!(
-            options.constructs.mdx_jsx_flow,
-            "should support `mdx` shortcut (3)"
-        );
-
-        assert_eq!(
-            format!("{:?}", ParseOptions::default()),
-            "ParseOptions { constructs: Constructs { attention: true, autolink: true, block_quote: true, character_escape: true, character_reference: true, code_indented: true, code_fenced: true, code_text: true, definition: true, frontmatter: false, gfm_autolink_literal: false, gfm_footnote_definition: false, gfm_label_start_footnote: false, gfm_strikethrough: false, gfm_table: false, gfm_task_list_item: false, hard_break_escape: true, hard_break_trailing: true, heading_atx: true, heading_setext: true, html_flow: true, html_text: true, label_start_image: true, label_start_link: true, label_end: true, list_item: true, math_flow: false, math_text: false, mdx_esm: false, mdx_expression_flow: false, mdx_expression_text: false, mdx_jsx_flow: false, mdx_jsx_text: false, thematic_break: true }, gfm_strikethrough_single_tilde: true, math_text_single_dollar: true, mdx_expression_parse: None, mdx_esm_parse: None }",
-            "should support `Debug` trait"
-        );
-        assert_eq!(
-            format!("{:?}", ParseOptions {
-                mdx_esm_parse: Some(Box::new(|_value| {
-                    MdxSignal::Ok
-                })),
-                mdx_expression_parse: Some(Box::new(|_value, _kind| {
-                    MdxSignal::Ok
-                })),
-                ..Default::default()
-            }),
-            "ParseOptions { constructs: Constructs { attention: true, autolink: true, block_quote: true, character_escape: true, character_reference: true, code_indented: true, code_fenced: true, code_text: true, definition: true, frontmatter: false, gfm_autolink_literal: false, gfm_footnote_definition: false, gfm_label_start_footnote: false, gfm_strikethrough: false, gfm_table: false, gfm_task_list_item: false, hard_break_escape: true, hard_break_trailing: true, heading_atx: true, heading_setext: true, html_flow: true, html_text: true, label_start_image: true, label_start_link: true, label_end: true, list_item: true, math_flow: false, math_text: false, mdx_esm: false, mdx_expression_flow: false, mdx_expression_text: false, mdx_jsx_flow: false, mdx_jsx_text: false, thematic_break: true }, gfm_strikethrough_single_tilde: true, math_text_single_dollar: true, mdx_expression_parse: Some(\"[Function]\"), mdx_esm_parse: Some(\"[Function]\") }",
-            "should support `Debug` trait on mdx functions"
-        );
-    }
-
-    #[test]
-    fn test_compile_options() {
-        CompileOptions::default();
-        CompileOptions::gfm();
-
-        let options = CompileOptions::default();
-        assert!(
-            !options.allow_dangerous_html,
-            "should default to safe `CommonMark` (1)"
-        );
-        assert!(
-            !options.gfm_tagfilter,
-            "should default to safe `CommonMark` (2)"
-        );
-
-        let options = CompileOptions::gfm();
-        assert!(
-            !options.allow_dangerous_html,
-            "should support safe `gfm` shortcut (1)"
-        );
-        assert!(
-            options.gfm_tagfilter,
-            "should support safe `gfm` shortcut (1)"
-        );
-    }
-
-    #[test]
-    fn test_options() {
-        Options::default();
-
-        let options = Options::default();
-        assert!(
-            options.parse.constructs.attention,
-            "should default to safe `CommonMark` (1)"
-        );
-        assert!(
-            !options.parse.constructs.gfm_autolink_literal,
-            "should default to safe `CommonMark` (2)"
-        );
-        assert!(
-            !options.parse.constructs.mdx_jsx_flow,
-            "should default to safe `CommonMark` (3)"
-        );
-        assert!(
-            !options.compile.allow_dangerous_html,
-            "should default to safe `CommonMark` (4)"
-        );
-
-        let options = Options::gfm();
-        assert!(
-            options.parse.constructs.attention,
-            "should support safe `gfm` shortcut (1)"
-        );
-        assert!(
-            options.parse.constructs.gfm_autolink_literal,
-            "should support safe `gfm` shortcut (2)"
-        );
-        assert!(
-            !options.parse.constructs.mdx_jsx_flow,
-            "should support safe `gfm` shortcut (3)"
-        );
-        assert!(
-            !options.compile.allow_dangerous_html,
-            "should support safe `gfm` shortcut (4)"
-        );
-    }
 
     #[test]
     fn test_to_html() {