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diff --git a/src/construct/code_indented.rs b/src/construct/code_indented.rs
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+//! Code (indented) is a construct that occurs in the flow content type.
+//!
+//! It forms with the following BNF:
+//!
+//! ```bnf
+//! code_indented ::= indented_filled_line *( eol *( blank_line eol ) indented_filled_line )
+//!
+//! ; Restriction: at least one `code` must not be whitespace.
+//! indented_filled_line ::= 4space_or_tab *code
+//! blank_line ::= *space_or_tab
+//! eol ::= '\r' | '\r\n' | '\n'
+//! code ::= . ; any unicode code point (other than line endings).
+//! space_or_tab ::= ' ' | '\t'
+//! ```
+//!
+//! Code (indented) relates to both the `<pre>` and the `<code>` elements in
+//! HTML.
+//! See [*§ 4.4.3 The `pre` element*][html-pre] and the [*§ 4.5.15 The `code`
+//! element*][html-code] in the HTML spec for more info.
+//!
+//! In markdown, it is also possible to use code (text) in the text content
+//! type.
+//! It is also possible to create code with the [code (fenced)][code-fenced]
+//! construct.
+//! That construct is more explicit, more similar to code (text), and has
+//! support for specifying the programming language that the code is in, so it
+//! is recommended to use that instead of indented code.
+//!
+//! ## References
+//!
+//! *   [`code-indented.js` in `micromark`](https://github.com/micromark/micromark/blob/main/packages/micromark-core-commonmark/dev/lib/code-indented.js)
+//! *   [*§ 4.4 Indented code blocks* in `CommonMark`](https://spec.commonmark.org/0.30/#indented-code-blocks)
+//!
+//! [code-fenced]: crate::construct::code_fenced
+//! [html-pre]: https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
+//! [html-code]: https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-code-element
+//!
+//! <!-- To do: link `flow`, `code_text` -->
+
+use crate::constant::TAB_SIZE;
+use crate::tokenizer::{Code, State, StateFnResult, TokenType, Tokenizer};
+
+/// Start of code (indented).
+///
+/// ```markdown
+/// |    asd
+/// ```
+pub fn start(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    match code {
+        Code::VirtualSpace | Code::Char(' ' | '\t') => {
+            tokenizer.enter(TokenType::CodeIndented);
+            tokenizer.enter(TokenType::CodeIndentedPrefixWhitespace);
+            indent(tokenizer, code, 0)
+        }
+        _ => (State::Nok, None),
+    }
+}
+
+/// Inside the initial whitespace.
+///
+/// ```markdown
+///  |   asd
+///   |  asd
+///    | asd
+///     |asd
+/// ```
+///
+/// > **Parsing note**: it is not needed to check if this first line is a
+/// > filled line (that it has a non-whitespace character), because blank lines
+/// > are parsed already, so we never run into that.
+fn indent(tokenizer: &mut Tokenizer, code: Code, size: usize) -> StateFnResult {
+    match code {
+        _ if size == TAB_SIZE => {
+            tokenizer.exit(TokenType::CodeIndentedPrefixWhitespace);
+            at_break(tokenizer, code)
+        }
+        Code::VirtualSpace | Code::Char(' ' | '\t') => {
+            tokenizer.consume(code);
+            (
+                State::Fn(Box::new(move |tokenizer, code| {
+                    indent(tokenizer, code, size + 1)
+                })),
+                None,
+            )
+        }
+        _ => (State::Nok, None),
+    }
+}
+
+/// At a break.
+///
+/// ```markdown
+///     |asd
+///     asd|
+/// ```
+fn at_break(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    match code {
+        Code::None => after(tokenizer, code),
+        Code::CarriageReturnLineFeed | Code::Char('\n' | '\r') => tokenizer
+            .attempt(further_start, |ok| {
+                Box::new(if ok { at_break } else { after })
+            })(tokenizer, code),
+        _ => {
+            tokenizer.enter(TokenType::CodeFlowChunk);
+            content(tokenizer, code)
+        }
+    }
+}
+
+/// Inside code content.
+///
+/// ```markdown
+///     |ab
+///     a|b
+///     ab|
+/// ```
+fn content(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    match code {
+        Code::None | Code::CarriageReturnLineFeed | Code::Char('\n' | '\r') => {
+            tokenizer.exit(TokenType::CodeFlowChunk);
+            at_break(tokenizer, code)
+        }
+        _ => {
+            tokenizer.consume(code);
+            (State::Fn(Box::new(content)), None)
+        }
+    }
+}
+
+/// After indented code.
+///
+/// ```markdown
+///     ab|
+/// ```
+fn after(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    tokenizer.exit(TokenType::CodeIndented);
+    (State::Ok, Some(vec![code]))
+}
+
+/// Right at a line ending, trying to parse another indent.
+///
+/// ```markdown
+///     ab|
+///     cd
+/// ```
+fn further_start(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    // To do: `nok` if lazy line.
+    match code {
+        Code::CarriageReturnLineFeed | Code::Char('\n' | '\r') => {
+            tokenizer.enter(TokenType::LineEnding);
+            tokenizer.consume(code);
+            tokenizer.exit(TokenType::LineEnding);
+            (State::Fn(Box::new(further_start)), None)
+        }
+        Code::VirtualSpace | Code::Char(' ' | '\t') => {
+            tokenizer.enter(TokenType::CodeIndentedPrefixWhitespace);
+            further_indent(tokenizer, code, 0)
+        }
+        _ => (State::Nok, None),
+    }
+}
+
+/// Inside further whitespace.
+///
+/// ```markdown
+///     asd
+///   |  asd
+/// ```
+fn further_indent(tokenizer: &mut Tokenizer, code: Code, size: usize) -> StateFnResult {
+    match code {
+        _ if size == TAB_SIZE => {
+            tokenizer.exit(TokenType::CodeIndentedPrefixWhitespace);
+            (State::Ok, Some(vec![code]))
+        }
+        Code::VirtualSpace | Code::Char(' ' | '\t') => {
+            tokenizer.consume(code);
+            (
+                State::Fn(Box::new(move |tokenizer, code| {
+                    further_indent(tokenizer, code, size + 1)
+                })),
+                None,
+            )
+        }
+        Code::CarriageReturnLineFeed | Code::Char('\n' | '\r') => {
+            tokenizer.exit(TokenType::CodeIndentedPrefixWhitespace);
+            further_start(tokenizer, code)
+        }
+        _ => (State::Nok, None),
+    }
+}