Fix to prefer flow over definitions, setext headings

An undocumented part of CommonMark is how to deal with things in definition
labels or definition titles (which both can span multiple lines).
Can flow (or containers?) interrupt them?
They can according to the `cmark` reference parser, so this was implemented here.

This adds a new `Content` content type, which houses zero or more definitions,
and then zero-or-one paragraphs.
Content can be followed by a setext heading underline, which either turns
into a setext heading when the content ends in a paragraph, or turns into
the start of the following paragraph when it is followed by content that
starts with a paragraph, or turns into a stray paragraph.

1 files changed, 21 insertions, 5 deletions

diff --git a/src/construct/definition.rs b/src/construct/definition.rs
index 1071489..8ccfb90 100644
--- a/src/construct/definition.rs
+++ b/src/construct/definition.rs
@@ -1,4 +1,4 @@
-//! Definition occurs in the [flow] content type.
+//! Definition occurs in the [content] content type.
 //!
 //! ## Grammar
 //!
@@ -12,8 +12,8 @@
 //! ; those parts.
 //! ```
 //!
-//! As this construct occurs in flow, like all flow constructs, it must be
-//! followed by an eol (line ending) or eof (end of file).
+//! This construct must be followed by an eol (line ending) or eof (end of
+//! file), like flow constructs.
 //!
 //! See [`destination`][destination], [`label`][label], and [`title`][title]
 //! for grammar, notes, and recommendations on each part.
@@ -88,7 +88,7 @@
 //! *   [`definition.js` in `micromark`](https://github.com/micromark/micromark/blob/main/packages/micromark-core-commonmark/dev/lib/definition.js)
 //! *   [*§ 4.7 Link reference definitions* in `CommonMark`](https://spec.commonmark.org/0.30/#link-reference-definitions)
 //!
-//! [flow]: crate::construct::flow
+//! [content]: crate::construct::content
 //! [string]: crate::construct::string
 //! [character_escape]: crate::construct::character_escape
 //! [character_reference]: crate::construct::character_reference
@@ -157,7 +157,10 @@ pub fn before(tokenizer: &mut Tokenizer) -> State {
             tokenizer.tokenize_state.token_1 = Name::DefinitionLabel;
             tokenizer.tokenize_state.token_2 = Name::DefinitionLabelMarker;
             tokenizer.tokenize_state.token_3 = Name::DefinitionLabelString;
-            tokenizer.attempt(State::Next(StateName::DefinitionLabelAfter), State::Nok);
+            tokenizer.attempt(
+                State::Next(StateName::DefinitionLabelAfter),
+                State::Next(StateName::DefinitionLabelNok),
+            );
             State::Retry(StateName::LabelStart)
         }
         _ => State::Nok,
@@ -192,6 +195,19 @@ pub fn label_after(tokenizer: &mut Tokenizer) -> State {
     }
 }
 
+/// At a non-label
+///
+/// ```markdown
+/// > | []
+///     ^
+/// ```
+pub fn label_nok(tokenizer: &mut Tokenizer) -> State {
+    tokenizer.tokenize_state.token_1 = Name::Data;
+    tokenizer.tokenize_state.token_2 = Name::Data;
+    tokenizer.tokenize_state.token_3 = Name::Data;
+    State::Nok
+}
+
 /// After marker.
 ///
 /// ```markdown