Reorganize to split util

13 files changed, 398 insertions, 375 deletions

diff --git a/src/compiler.rs b/src/compiler.rs
index 619bbe5..e1ce440 100644
--- a/src/compiler.rs
+++ b/src/compiler.rs
@@ -2,8 +2,10 @@
 use crate::construct::character_reference::Kind as CharacterReferenceKind;
 use crate::tokenizer::{Code, Event, EventType, TokenType};
 use crate::util::{
-    decode_named_character_reference, decode_numeric_character_reference, encode, get_span,
-    sanitize_uri, slice_serialize,
+    decode_character_reference::{decode_named, decode_numeric},
+    encode::encode,
+    sanitize_uri::sanitize_uri,
+    span::{from_exit_event, serialize},
 };
 
 /// Configuration (optional).
@@ -141,7 +143,7 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                     ignore_encode = false;
                 }
                 TokenType::HtmlFlowData | TokenType::HtmlTextData => {
-                    let slice = slice_serialize(codes, &get_span(events, index), false);
+                    let slice = serialize(codes, &from_exit_event(events, index), false);
 
                     let res = if ignore_encode { slice } else { encode(&slice) };
 
@@ -208,9 +210,9 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                 }
                 TokenType::CodeFlowChunk => {
                     code_flow_seen_data = Some(true);
-                    buf_tail_mut(buffers).push(encode(&slice_serialize(
+                    buf_tail_mut(buffers).push(encode(&serialize(
                         codes,
-                        &get_span(events, index),
+                        &from_exit_event(events, index),
                         false,
                     )));
                 }
@@ -224,13 +226,17 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                     if let Some(buf) = atx_heading_buffer {
                         atx_heading_buffer = Some(
                             buf.to_string()
-                                + &encode(&slice_serialize(codes, &get_span(events, index), false)),
+                                + &encode(&serialize(
+                                    codes,
+                                    &from_exit_event(events, index),
+                                    false,
+                                )),
                         );
                     }
 
                     // First fence we see.
                     if None == atx_opening_sequence_size {
-                        let rank = slice_serialize(codes, &get_span(events, index), false).len();
+                        let rank = serialize(codes, &from_exit_event(events, index), false).len();
                         atx_opening_sequence_size = Some(rank);
                         buf_tail_mut(buffers).push(format!("<h{}>", rank));
                     }
@@ -246,7 +252,7 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                         atx_heading_buffer = Some("".to_string());
                     }
 
-                    let slice = encode(&slice_serialize(codes, &get_span(events, index), false));
+                    let slice = encode(&serialize(codes, &from_exit_event(events, index), false));
                     println!("slice: {:?}", slice);
                     buf_tail_mut(buffers).push(slice);
                 }
@@ -258,7 +264,7 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                     atx_heading_buffer = None;
                 }
                 TokenType::AutolinkProtocol => {
-                    let slice = slice_serialize(codes, &get_span(events, index), false);
+                    let slice = serialize(codes, &from_exit_event(events, index), false);
                     let buf = buf_tail_mut(buffers);
                     buf.push(format!(
                         "<a href=\"{}\">",
@@ -268,7 +274,7 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                     buf.push("</a>".to_string());
                 }
                 TokenType::AutolinkEmail => {
-                    let slice = slice_serialize(codes, &get_span(events, index), false);
+                    let slice = serialize(codes, &from_exit_event(events, index), false);
                     let buf = buf_tail_mut(buffers);
                     buf.push(format!(
                         "<a href=\"mailto:{}\">",
@@ -289,9 +295,9 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                     // } else if code_text_inside {
                     //     buf_tail_mut(buffers).push(" ".to_string());
                     } else {
-                        buf_tail_mut(buffers).push(encode(&slice_serialize(
+                        buf_tail_mut(buffers).push(encode(&serialize(
                             codes,
-                            &get_span(events, index),
+                            &from_exit_event(events, index),
                             false,
                         )));
                     }
@@ -308,18 +314,16 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                 TokenType::CharacterReferenceValue => {
                     let kind = character_reference_kind
                         .expect("expected `character_reference_kind` to be set");
-                    let reference = slice_serialize(codes, &get_span(events, index), false);
+                    let reference = serialize(codes, &from_exit_event(events, index), false);
                     let ref_string = reference.as_str();
                     let value = match kind {
                         CharacterReferenceKind::Decimal => {
-                            decode_numeric_character_reference(ref_string, 10).to_string()
+                            decode_numeric(ref_string, 10).to_string()
                         }
                         CharacterReferenceKind::Hexadecimal => {
-                            decode_numeric_character_reference(ref_string, 16).to_string()
-                        }
-                        CharacterReferenceKind::Named => {
-                            decode_named_character_reference(ref_string)
+                            decode_numeric(ref_string, 16).to_string()
                         }
+                        CharacterReferenceKind::Named => decode_named(ref_string),
                     };
 
                     buf_tail_mut(buffers).push(value);
@@ -329,9 +333,9 @@ pub fn compile(events: &[Event], codes: &[Code], options: &CompileOptions) -> St
                 // This branch below currently acts as the resulting `data` tokens.
                 TokenType::Data | TokenType::CharacterEscapeValue => {
                     // last_was_tag = false;
-                    buf_tail_mut(buffers).push(encode(&slice_serialize(
+                    buf_tail_mut(buffers).push(encode(&serialize(
                         codes,
-                        &get_span(events, index),
+                        &from_exit_event(events, index),
                         false,
                     )));
                 }
diff --git a/src/construct/character_reference.rs b/src/construct/character_reference.rs
index 943d70f..ba2ad61 100644
--- a/src/construct/character_reference.rs
+++ b/src/construct/character_reference.rs
@@ -20,7 +20,7 @@
 //! However, for security reasons, several numeric character references parse
 //! fine but are not rendered as their corresponding character and they are
 //! instead replaced by a U+FFFD REPLACEMENT CHARACTER (`�`).
-//! See [`decode_numeric_character_reference`][decode_numeric] for more info.
+//! See [`decode_numeric`][decode_numeric] for more info.
 //!
 //! To escape ASCII punctuation characters, use the terser
 //! [character escape][character_escape] construct instead (as in, `\&`).
@@ -48,7 +48,7 @@
 //! [string]: crate::content::string
 //! [text]: crate::content::text
 //! [character_escape]: crate::construct::character_reference
-//! [decode_numeric]: crate::util::decode_numeric_character_reference
+//! [decode_numeric]: crate::util::decode_character_reference::decode_numeric
 //! [character_reference_names]: crate::constant::CHARACTER_REFERENCE_NAMES
 //! [html]: https://html.spec.whatwg.org/multipage/parsing.html#character-reference-state
 //!
diff --git a/src/construct/code_fenced.rs b/src/construct/code_fenced.rs
index a440d40..c852e8d 100644
--- a/src/construct/code_fenced.rs
+++ b/src/construct/code_fenced.rs
@@ -91,7 +91,7 @@
 use crate::constant::{CODE_FENCED_SEQUENCE_SIZE_MIN, TAB_SIZE};
 use crate::construct::partial_whitespace::start as whitespace;
 use crate::tokenizer::{Code, State, StateFnResult, TokenType, Tokenizer};
-use crate::util::get_span;
+use crate::util::span::from_exit_event;
 
 /// Kind of fences.
 #[derive(Debug, Clone, PartialEq)]
@@ -147,7 +147,7 @@ fn before_sequence_open(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult
 
     if let Some(event) = tail {
         if event.token_type == TokenType::Whitespace {
-            let span = get_span(&tokenizer.events, tokenizer.events.len() - 1);
+            let span = from_exit_event(&tokenizer.events, tokenizer.events.len() - 1);
             prefix = span.end_index - span.start_index;
         }
     }
@@ -415,7 +415,7 @@ fn close_sequence_before(tokenizer: &mut Tokenizer, info: Info, code: Code) -> S
 
     if let Some(event) = tail {
         if event.token_type == TokenType::Whitespace {
-            let span = get_span(&tokenizer.events, tokenizer.events.len() - 1);
+            let span = from_exit_event(&tokenizer.events, tokenizer.events.len() - 1);
             prefix = span.end_index - span.start_index;
         }
     }
diff --git a/src/construct/mod.rs b/src/construct/mod.rs
index d2203d2..14f53a0 100644
--- a/src/construct/mod.rs
+++ b/src/construct/mod.rs
@@ -53,7 +53,6 @@
 //! example `ascii_punctuation` refers to
 //! [`char::is_ascii_punctuation`][char::is_ascii_punctuation].
 
-
 pub mod autolink;
 pub mod blank_line;
 pub mod character_escape;
diff --git a/src/content/flow.rs b/src/content/flow.rs
index 6fa8c25..4d2ece1 100644
--- a/src/content/flow.rs
+++ b/src/content/flow.rs
@@ -28,7 +28,7 @@ use crate::construct::{
 };
 use crate::subtokenize::subtokenize;
 use crate::tokenizer::{Code, Event, Point, State, StateFnResult, TokenType, Tokenizer};
-use crate::util::get_span;
+use crate::util::span::from_exit_event;
 
 /// Turn `codes` as the flow content type into events.
 pub fn flow(codes: &[Code], point: Point, index: usize) -> Vec<Event> {
@@ -240,7 +240,7 @@ fn continuation_construct_after_prefix(tokenizer: &mut Tokenizer, code: Code) ->
 
     if let Some(event) = tail {
         if event.token_type == TokenType::Whitespace {
-            let span = get_span(&tokenizer.events, tokenizer.events.len() - 1);
+            let span = from_exit_event(&tokenizer.events, tokenizer.events.len() - 1);
             prefix = span.end_index - span.start_index;
         }
     }
diff --git a/src/subtokenize.rs b/src/subtokenize.rs
index e004f7b..35d7672 100644
--- a/src/subtokenize.rs
+++ b/src/subtokenize.rs
@@ -1,10 +1,8 @@
-use crate::content::content::start as content;
-use crate::content::string::start as string;
-use crate::content::text::start as text;
+use crate::content::{content::start as content, string::start as string, text::start as text};
 use crate::tokenizer::{
     Code, Event, EventType, State, StateFn, StateFnResult, TokenType, Tokenizer,
 };
-use crate::util::{slice_codes, Span};
+use crate::util::span;
 use std::collections::HashMap;
 
 /// To do.
@@ -51,7 +49,7 @@ pub fn subtokenize(events: Vec<Event>, codes: &[Code]) -> (Vec<Event>, bool) {
             while let Some(index_ptr) = index_opt {
                 let enter = &events[index_ptr];
                 assert_eq!(enter.event_type, EventType::Enter);
-                let span = Span {
+                let span = span::Span {
                     start_index: enter.index,
                     end_index: events[index_ptr + 1].index,
                 };
@@ -66,7 +64,7 @@ pub fn subtokenize(events: Vec<Event>, codes: &[Code]) -> (Vec<Event>, bool) {
                     _ => unreachable!("cannot be ok/nok"),
                 };
 
-                result = tokenizer.feed(slice_codes(codes, &span), func, enter.next == None);
+                result = tokenizer.feed(span::codes(codes, &span), func, enter.next == None);
 
                 if let Some(ref x) = result.1 {
                     if !x.is_empty() {
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index 8a2f477..486bc75 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -513,6 +513,8 @@ impl Tokenizer {
         let mut state = State::Fn(Box::new(start));
         let mut index = 0;
 
+        println!("feed: {:?} {:?}", codes, drain);
+
         self.consumed = true;
 
         while index < codes.len() {
diff --git a/src/util.rs b/src/util.rs
deleted file mode 100644
index accc48e..0000000
--- a/src/util.rs
+++ /dev/null
@@ -1,341 +0,0 @@
-//! Some utilities helpful when parsing and compiling markdown.
-
-use crate::constant::{CHARACTER_REFERENCE_NAMES, CHARACTER_REFERENCE_VALUES};
-use crate::tokenizer::{Code, Event, EventType};
-
-/// Encode dangerous html characters.
-///
-/// This ensures that certain characters which have special meaning in HTML are
-/// dealt with.
-/// Technically, we can skip `>` and `"` in many cases, but CM includes them.
-///
-/// This behavior is not explained in prose in `CommonMark` but can be inferred
-/// from the input/output test cases.
-///
-/// ## Examples
-///
-/// ```rust ignore
-/// use micromark::util::encode;
-///
-/// assert_eq!(encode("I <3 🦀"), "I &lt;3 🦀");
-/// ```
-///
-/// ## References
-///
-/// *   [`micromark-util-encode` in `micromark`](https://github.com/micromark/micromark/tree/main/packages/micromark-util-encode)
-pub fn encode(value: &str) -> String {
-    value
-        .replace('&', "&amp;")
-        .replace('"', "&quot;")
-        .replace('<', "&lt;")
-        .replace('>', "&gt;")
-}
-
-/// Make a value safe for injection as a URL.
-///
-/// This encodes unsafe characters with percent-encoding and skips already
-/// encoded sequences (see `normalize_uri` below).
-/// Further unsafe characters are encoded as character references (see
-/// `encode`).
-///
-/// Then, a vec of (lowercase) allowed protocols can be given, in which case
-/// the URL is sanitized.
-///
-/// For example, `Some(vec!["http", "https", "irc", "ircs", "mailto", "xmpp"])`
-/// can be used for `a[href]`, or `Some(vec!["http", "https"])` for `img[src]`.
-/// If the URL includes an unknown protocol (one not matched by `protocol`, such
-/// as a dangerous example, `javascript:`), the value is ignored.
-pub fn sanitize_uri(value: &str, protocols: &Option<Vec<&str>>) -> String {
-    let value = encode(&normalize_uri(value));
-
-    if let Some(protocols) = protocols {
-        let chars: Vec<char> = value.chars().collect();
-        let mut index = 0;
-        let mut colon: Option<usize> = None;
-
-        while index < chars.len() {
-            let char = chars[index];
-
-            match char {
-                ':' => {
-                    colon = Some(index);
-                    break;
-                }
-                '?' | '#' | '/' => break,
-                _ => {}
-            }
-
-            index += 1;
-        }
-
-        // If there is no protocol, or the first colon is after `?`, `#`, or `/`, it’s relative.
-        // It is a protocol, it should be allowed.
-        if let Some(colon) = colon {
-            let protocol = chars[0..colon].iter().collect::<String>().to_lowercase();
-            if !protocols.contains(&protocol.as_str()) {
-                return "".to_string();
-            }
-        }
-    }
-
-    value
-}
-
-/// Normalize a URL (such as used in definitions).
-///
-/// Encode unsafe characters with percent-encoding, skipping already encoded
-/// sequences.
-fn normalize_uri(value: &str) -> String {
-    let chars: Vec<char> = value.chars().collect();
-    let mut result: Vec<String> = vec![];
-    let mut index = 0;
-    let mut start = 0;
-    let mut buff = [0; 4];
-
-    while index < chars.len() {
-        let char = chars[index];
-
-        // A correct percent encoded value.
-        if char == '%'
-            && index + 2 < chars.len()
-            && chars[index + 1].is_ascii_alphanumeric()
-            && chars[index + 2].is_ascii_alphanumeric()
-        {
-            index += 3;
-            continue;
-        }
-
-        // Note: Rust already takes care of lone astral surrogates.
-        // Non-ascii or not allowed ascii.
-        if char >= '\u{0080}'
-            || !matches!(char, '!' | '#' | '$' | '&'..=';' | '=' | '?'..='Z' | '_' | 'a'..='z' | '~')
-        {
-            result.push(chars[start..index].iter().collect::<String>());
-
-            char.encode_utf8(&mut buff);
-            result.push(
-                buff[0..char.len_utf8()]
-                    .iter()
-                    .map(|&byte| format!("%{:X}", byte))
-                    .collect::<String>(),
-            );
-
-            start = index + 1;
-        }
-
-        index += 1;
-    }
-
-    result.push(chars[start..].iter().collect::<String>());
-
-    result.join("")
-}
-
-/// Decode numeric character references.
-///
-/// Turn the number (in string form as either hexadecimal or decimal) coming
-/// from a numeric character reference into a character.
-/// Whether the base of the string form is `10` (decimal) or `16` (hexadecimal)
-/// must be passed as the `radix` parameter.
-///
-/// This returns the `char` associated with that number or a replacement
-/// character for C0 control characters (except for ASCII whitespace), C1
-/// control characters, lone surrogates, noncharacters, and out of range
-/// characters.
-///
-/// ## Examples
-///
-/// ```rust ignore
-/// use micromark::util::decode_numeric_character_reference;
-///
-/// assert_eq!(decode_numeric_character_reference("123", 10), '{');
-/// assert_eq!(decode_numeric_character_reference("9", 16), '\t');
-/// assert_eq!(decode_numeric_character_reference("0", 10), '�'); // Not allowed.
-/// ```
-///
-/// ## Panics
-///
-/// This function panics if a invalid string or an out of bounds valid string
-/// is given.
-/// It is expected that figuring out whether a number is allowed is handled in
-/// the parser.
-/// When `micromark` is used, this function never panics.
-///
-/// ## References
-///
-/// *   [`micromark-util-decode-numeric-character-reference` in `micromark`](https://github.com/micromark/micromark/tree/main/packages/micromark-util-decode-numeric-character-reference)
-/// *   [*§ 2.5 Entity and numeric character references* in `CommonMark`](https://spec.commonmark.org/0.30/#entity-and-numeric-character-references)
-pub fn decode_numeric_character_reference(value: &str, radix: u32) -> char {
-    let code = u32::from_str_radix(value, radix).expect("expected `value` to be an int");
-
-    if
-    // C0 except for HT, LF, FF, CR, space
-    code < 0x09 ||
-    code == 0x0B ||
-    (code > 0x0D && code < 0x20) ||
-    // Control character (DEL) of the basic block and C1 controls.
-    (code > 0x7E && code < 0xA0) ||
-    // Lone high surrogates and low surrogates.
-    (code > 0xd7ff && code < 0xe000) ||
-    // Noncharacters.
-    (code > 0xfdcf && code < 0xfdf0) ||
-    ((code & 0xffff) == 0xffff) ||
-    ((code & 0xffff) == 0xfffe) ||
-    // Out of range
-    code > 0x0010_ffff
-    {
-        '�'
-    } else {
-        char::from_u32(code).expect("expected valid `code`")
-    }
-}
-
-/// Decode named character references.
-///
-/// Turn the name coming from a named character reference (without the `&` or
-/// `;`) into a string.
-/// This looks the given string up in [`CHARACTER_REFERENCE_NAMES`][] and then
-/// takes the corresponding value from [`CHARACTER_REFERENCE_VALUES`][].
-///
-/// The result is `String` instead of `char` because named character references
-/// can expand into multiple characters.
-///
-/// ## Examples
-///
-/// ```rust ignore
-/// use micromark::util::decode_named_character_reference;
-///
-/// assert_eq!(decode_named_character_reference("amp"), "&");
-/// assert_eq!(decode_named_character_reference("AElig"), "Æ");
-/// assert_eq!(decode_named_character_reference("aelig"), "æ");
-/// ```
-///
-/// ## Panics
-///
-/// This function panics if a name not in [`CHARACTER_REFERENCE_NAMES`][] is
-/// given.
-/// It is expected that figuring out whether a name is allowed is handled in
-/// the parser.
-/// When `micromark` is used, this function never panics.
-///
-/// ## References
-///
-/// *   [`wooorm/decode-named-character-reference`](https://github.com/wooorm/decode-named-character-reference)
-/// *   [*§ 2.5 Entity and numeric character references* in `CommonMark`](https://spec.commonmark.org/0.30/#entity-and-numeric-character-references)
-pub fn decode_named_character_reference(value: &str) -> String {
-    let position = CHARACTER_REFERENCE_NAMES.iter().position(|&x| x == value);
-    if let Some(index) = position {
-        CHARACTER_REFERENCE_VALUES[index].to_string()
-    } else {
-        unreachable!("expected valid `name`")
-    }
-}
-
-/// A struct representing the span of an opening and closing event of a token.
-#[derive(Debug)]
-pub struct Span {
-    // To do: probably needed in the future.
-    // start: Point,
-    /// Absolute offset (and `index` in `codes`) of where this span starts.
-    pub start_index: usize,
-    // To do: probably needed in the future.
-    // end: Point,
-    /// Absolute offset (and `index` in `codes`) of where this span ends.
-    pub end_index: usize,
-    // To do: probably needed in the future.
-    // token_type: TokenType,
-}
-
-/// Get a span from an event.
-///
-/// Get the span of an `exit` event, by looking backwards through the events to
-/// find the corresponding `enter` event.
-/// This assumes that tokens with the same are not nested.
-///
-/// ## Panics
-///
-/// This function panics if an enter event is given.
-/// When `micromark` is used, this function never panics.
-pub fn get_span(events: &[Event], index: usize) -> Span {
-    let exit = &events[index];
-    // let end = exit.point.clone();
-    let end_index = exit.index;
-    let token_type = exit.token_type.clone();
-    // To do: support `enter` events if needed and walk forwards?
-    assert_eq!(
-        exit.event_type,
-        EventType::Exit,
-        "expected `get_span` to be called on `exit` event"
-    );
-    let mut enter_index = index - 1;
-
-    loop {
-        let enter = &events[enter_index];
-        if enter.event_type == EventType::Enter && enter.token_type == token_type {
-            return Span {
-                // start: enter.point.clone(),
-                start_index: enter.index,
-                // end,
-                end_index,
-                // token_type,
-            };
-        }
-
-        enter_index -= 1;
-    }
-}
-
-/// Serialize a span, optionally expanding tabs.
-pub fn slice_serialize(codes: &[Code], span: &Span, expand_tabs: bool) -> String {
-    serialize_chunks(slice_codes(codes, span), expand_tabs)
-}
-
-/// Get a slice of codes from a span.
-pub fn slice_codes<'a>(codes: &'a [Code], span: &Span) -> &'a [Code] {
-    &codes[span.start_index..span.end_index]
-}
-
-/// Serialize a slice of codes, optionally expanding tabs.
-pub fn serialize_chunks(codes: &[Code], expand_tabs: bool) -> String {
-    let mut at_tab = false;
-    let mut index = 0;
-    let mut value: Vec<char> = vec![];
-
-    while index < codes.len() {
-        let code = codes[index];
-        let mut at_tab_next = false;
-
-        match code {
-            Code::CarriageReturnLineFeed => {
-                value.push('\r');
-                value.push('\n');
-            }
-            Code::Char(char) if char == '\n' || char == '\r' => {
-                value.push(char);
-            }
-            Code::Char(char) if char == '\t' => {
-                at_tab_next = true;
-                value.push(if expand_tabs { ' ' } else { char });
-            }
-            Code::VirtualSpace => {
-                if !expand_tabs && at_tab {
-                    index += 1;
-                    continue;
-                }
-                value.push(' ');
-            }
-            Code::Char(char) => {
-                value.push(char);
-            }
-            Code::None => {
-                unreachable!("unexpected EOF code in codes");
-            }
-        }
-
-        at_tab = at_tab_next;
-
-        index += 1;
-    }
-
-    value.into_iter().collect()
-}
diff --git a/src/util/decode_character_reference.rs b/src/util/decode_character_reference.rs
new file mode 100644
index 0000000..4a9317e
--- /dev/null
+++ b/src/util/decode_character_reference.rs
@@ -0,0 +1,103 @@
+//! Utilities to decode character references.
+
+use crate::constant::{CHARACTER_REFERENCE_NAMES, CHARACTER_REFERENCE_VALUES};
+
+/// Decode named character references.
+///
+/// Turn the name coming from a named character reference (without the `&` or
+/// `;`) into a string.
+/// This looks the given string up in [`CHARACTER_REFERENCE_NAMES`][] and then
+/// takes the corresponding value from [`CHARACTER_REFERENCE_VALUES`][].
+///
+/// The result is `String` instead of `char` because named character references
+/// can expand into multiple characters.
+///
+/// ## Examples
+///
+/// ```rust ignore
+/// use micromark::util::character_reference::decode_named;
+///
+/// assert_eq!(decode_named("amp"), "&");
+/// assert_eq!(decode_named("AElig"), "Æ");
+/// assert_eq!(decode_named("aelig"), "æ");
+/// ```
+///
+/// ## Panics
+///
+/// This function panics if a name not in [`CHARACTER_REFERENCE_NAMES`][] is
+/// given.
+/// It is expected that figuring out whether a name is allowed is handled in
+/// the parser.
+/// When `micromark` is used, this function never panics.
+///
+/// ## References
+///
+/// *   [`wooorm/decode-named-character-reference`](https://github.com/wooorm/decode-named-character-reference)
+/// *   [*§ 2.5 Entity and numeric character references* in `CommonMark`](https://spec.commonmark.org/0.30/#entity-and-numeric-character-references)
+pub fn decode_named(value: &str) -> String {
+    let position = CHARACTER_REFERENCE_NAMES.iter().position(|&x| x == value);
+    if let Some(index) = position {
+        CHARACTER_REFERENCE_VALUES[index].to_string()
+    } else {
+        unreachable!("expected valid `name`")
+    }
+}
+
+/// Decode numeric character references.
+///
+/// Turn the number (in string form as either hexadecimal or decimal) coming
+/// from a numeric character reference into a character.
+/// Whether the base of the string form is `10` (decimal) or `16` (hexadecimal)
+/// must be passed as the `radix` parameter.
+///
+/// This returns the `char` associated with that number or a replacement
+/// character for C0 control characters (except for ASCII whitespace), C1
+/// control characters, lone surrogates, noncharacters, and out of range
+/// characters.
+///
+/// ## Examples
+///
+/// ```rust ignore
+/// use micromark::util::character_reference::decode_numeric;
+///
+/// assert_eq!(decode_numeric("123", 10), '{');
+/// assert_eq!(decode_numeric("9", 16), '\t');
+/// assert_eq!(decode_numeric("0", 10), '�'); // Not allowed.
+/// ```
+///
+/// ## Panics
+///
+/// This function panics if a invalid string or an out of bounds valid string
+/// is given.
+/// It is expected that figuring out whether a number is allowed is handled in
+/// the parser.
+/// When `micromark` is used, this function never panics.
+///
+/// ## References
+///
+/// *   [`micromark-util-decode-numeric-character-reference` in `micromark`](https://github.com/micromark/micromark/tree/main/packages/micromark-util-decode-numeric-character-reference)
+/// *   [*§ 2.5 Entity and numeric character references* in `CommonMark`](https://spec.commonmark.org/0.30/#entity-and-numeric-character-references)
+pub fn decode_numeric(value: &str, radix: u32) -> char {
+    let code = u32::from_str_radix(value, radix).expect("expected `value` to be an int");
+
+    if
+    // C0 except for HT, LF, FF, CR, space
+    code < 0x09 ||
+    code == 0x0B ||
+    (code > 0x0D && code < 0x20) ||
+    // Control character (DEL) of the basic block and C1 controls.
+    (code > 0x7E && code < 0xA0) ||
+    // Lone high surrogates and low surrogates.
+    (code > 0xd7ff && code < 0xe000) ||
+    // Noncharacters.
+    (code > 0xfdcf && code < 0xfdf0) ||
+    ((code & 0xffff) == 0xffff) ||
+    ((code & 0xffff) == 0xfffe) ||
+    // Out of range
+    code > 0x0010_ffff
+    {
+        '�'
+    } else {
+        char::from_u32(code).expect("expected valid `code`")
+    }
+}
diff --git a/src/util/encode.rs b/src/util/encode.rs
new file mode 100644
index 0000000..f79c8ea
--- /dev/null
+++ b/src/util/encode.rs
@@ -0,0 +1,29 @@
+//! Utilities to encode HTML.
+
+/// Encode dangerous html characters.
+///
+/// This ensures that certain characters which have special meaning in HTML are
+/// dealt with.
+/// Technically, we can skip `>` and `"` in many cases, but CM includes them.
+///
+/// This behavior is not explained in prose in `CommonMark` but can be inferred
+/// from the input/output test cases.
+///
+/// ## Examples
+///
+/// ```rust ignore
+/// use micromark::util::encode;
+///
+/// assert_eq!(encode("I <3 🦀"), "I &lt;3 🦀");
+/// ```
+///
+/// ## References
+///
+/// *   [`micromark-util-encode` in `micromark`](https://github.com/micromark/micromark/tree/main/packages/micromark-util-encode)
+pub fn encode(value: &str) -> String {
+    value
+        .replace('&', "&amp;")
+        .replace('"', "&quot;")
+        .replace('<', "&lt;")
+        .replace('>', "&gt;")
+}
diff --git a/src/util/mod.rs b/src/util/mod.rs
new file mode 100644
index 0000000..c3db267
--- /dev/null
+++ b/src/util/mod.rs
@@ -0,0 +1,6 @@
+//! Utilities used when compiling markdown.
+
+pub mod decode_character_reference;
+pub mod encode;
+pub mod sanitize_uri;
+pub mod span;
diff --git a/src/util/sanitize_uri.rs b/src/util/sanitize_uri.rs
new file mode 100644
index 0000000..1dffc50
--- /dev/null
+++ b/src/util/sanitize_uri.rs
@@ -0,0 +1,111 @@
+//! Utilities to make urls safe.
+
+use crate::util::encode::encode;
+
+/// Make a value safe for injection as a URL.
+///
+/// This encodes unsafe characters with percent-encoding and skips already
+/// encoded sequences (see `normalize_uri` below).
+/// Further unsafe characters are encoded as character references (see
+/// `encode`).
+///
+/// Then, a vec of (lowercase) allowed protocols can be given, in which case
+/// the URL is sanitized.
+///
+/// For example, `Some(vec!["http", "https", "irc", "ircs", "mailto", "xmpp"])`
+/// can be used for `a[href]`, or `Some(vec!["http", "https"])` for `img[src]`.
+/// If the URL includes an unknown protocol (one not matched by `protocol`, such
+/// as a dangerous example, `javascript:`), the value is ignored.
+///
+/// ## References
+///
+/// *   [`micromark-util-sanitize-uri` in `micromark`](https://github.com/micromark/micromark/tree/main/packages/micromark-util-sanitize-uri)
+pub fn sanitize_uri(value: &str, protocols: &Option<Vec<&str>>) -> String {
+    let value = encode(&normalize_uri(value));
+
+    if let Some(protocols) = protocols {
+        let chars: Vec<char> = value.chars().collect();
+        let mut index = 0;
+        let mut colon: Option<usize> = None;
+
+        while index < chars.len() {
+            let char = chars[index];
+
+            match char {
+                ':' => {
+                    colon = Some(index);
+                    break;
+                }
+                '?' | '#' | '/' => break,
+                _ => {}
+            }
+
+            index += 1;
+        }
+
+        // If there is no protocol, or the first colon is after `?`, `#`, or `/`, it’s relative.
+        // It is a protocol, it should be allowed.
+        if let Some(colon) = colon {
+            let protocol = chars[0..colon].iter().collect::<String>().to_lowercase();
+            if !protocols.contains(&protocol.as_str()) {
+                return "".to_string();
+            }
+        }
+    }
+
+    value
+}
+
+/// Normalize a URL (such as used in definitions).
+///
+/// Encode unsafe characters with percent-encoding, skipping already encoded
+/// sequences.
+///
+/// ## References
+///
+/// *   [`micromark-util-sanitize-uri` in `micromark`](https://github.com/micromark/micromark/tree/main/packages/micromark-util-sanitize-uri)
+fn normalize_uri(value: &str) -> String {
+    let chars: Vec<char> = value.chars().collect();
+    let mut result: Vec<String> = vec![];
+    let mut index = 0;
+    let mut start = 0;
+    let mut buff = [0; 4];
+
+    while index < chars.len() {
+        let char = chars[index];
+
+        // A correct percent encoded value.
+        if char == '%'
+            && index + 2 < chars.len()
+            && chars[index + 1].is_ascii_alphanumeric()
+            && chars[index + 2].is_ascii_alphanumeric()
+        {
+            index += 3;
+            continue;
+        }
+
+        // Note: Rust already takes care of lone astral surrogates.
+        // Non-ascii or not allowed ascii.
+        if char >= '\u{0080}'
+            || !matches!(char, '!' | '#' | '$' | '&'..=';' | '=' | '?'..='Z' | '_' | 'a'..='z' | '~')
+        {
+            result.push(chars[start..index].iter().collect::<String>());
+
+            char.encode_utf8(&mut buff);
+            result.push(
+                buff[0..char.len_utf8()]
+                    .iter()
+                    .map(|&byte| format!("%{:X}", byte))
+                    .collect::<String>(),
+            );
+
+            start = index + 1;
+        }
+
+        index += 1;
+    }
+
+    result.push(chars[start..].iter().collect::<String>());
+
+    result.join("")
+}
diff --git a/src/util/span.rs b/src/util/span.rs
new file mode 100644
index 0000000..c48549b
--- /dev/null
+++ b/src/util/span.rs
@@ -0,0 +1,112 @@
+//! Utilities to deal with semantic labels.
+
+use crate::tokenizer::{Code, Event, EventType};
+
+/// A struct representing the span of an opening and closing event of a token.
+#[derive(Debug)]
+pub struct Span {
+    // To do: probably needed in the future.
+    // start: Point,
+    /// Absolute offset (and `index` in `codes`) of where this span starts.
+    pub start_index: usize,
+    // To do: probably needed in the future.
+    // end: Point,
+    /// Absolute offset (and `index` in `codes`) of where this span ends.
+    pub end_index: usize,
+    // To do: probably needed in the future.
+    // token_type: TokenType,
+}
+
+/// Get a span from an event.
+///
+/// Get the span of an `exit` event, by looking backwards through the events to
+/// find the corresponding `enter` event.
+/// This assumes that tokens with the same are not nested.
+///
+/// ## Panics
+///
+/// This function panics if an enter event is given.
+/// When `micromark` is used, this function never panics.
+pub fn from_exit_event(events: &[Event], index: usize) -> Span {
+    let exit = &events[index];
+    // let end = exit.point.clone();
+    let end_index = exit.index;
+    let token_type = exit.token_type.clone();
+    // To do: support `enter` events if needed and walk forwards?
+    assert_eq!(
+        exit.event_type,
+        EventType::Exit,
+        "expected `get_span` to be called on `exit` event"
+    );
+    let mut enter_index = index - 1;
+
+    loop {
+        let enter = &events[enter_index];
+        if enter.event_type == EventType::Enter && enter.token_type == token_type {
+            return Span {
+                // start: enter.point.clone(),
+                start_index: enter.index,
+                // end,
+                end_index,
+                // token_type,
+            };
+        }
+
+        enter_index -= 1;
+    }
+}
+
+/// Serialize a span, optionally expanding tabs.
+pub fn serialize(all_codes: &[Code], span: &Span, expand_tabs: bool) -> String {
+    serialize_codes(codes(all_codes, span), expand_tabs)
+}
+
+/// Get a slice of codes from a span.
+pub fn codes<'a>(codes: &'a [Code], span: &Span) -> &'a [Code] {
+    &codes[span.start_index..span.end_index]
+}
+
+/// Serialize a slice of codes, optionally expanding tabs.
+fn serialize_codes(codes: &[Code], expand_tabs: bool) -> String {
+    let mut at_tab = false;
+    let mut index = 0;
+    let mut value: Vec<char> = vec![];
+
+    while index < codes.len() {
+        let code = codes[index];
+        let mut at_tab_next = false;
+
+        match code {
+            Code::CarriageReturnLineFeed => {
+                value.push('\r');
+                value.push('\n');
+            }
+            Code::Char(char) if char == '\n' || char == '\r' => {
+                value.push(char);
+            }
+            Code::Char(char) if char == '\t' => {
+                at_tab_next = true;
+                value.push(if expand_tabs { ' ' } else { char });
+            }
+            Code::VirtualSpace => {
+                if !expand_tabs && at_tab {
+                    index += 1;
+                    continue;
+                }
+                value.push(' ');
+            }
+            Code::Char(char) => {
+                value.push(char);
+            }
+            Code::None => {
+                unreachable!("unexpected EOF code in codes");
+            }
+        }
+
+        at_tab = at_tab_next;
+
+        index += 1;
+    }
+
+    value.into_iter().collect()
+}