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, 5 insertions, 2 deletions

diff --git a/src/construct/heading_atx.rs b/src/construct/heading_atx.rs
index c1090c4..b76e455 100644
--- a/src/construct/heading_atx.rs
+++ b/src/construct/heading_atx.rs
@@ -66,9 +66,10 @@ use crate::construct::partial_space_or_tab::{space_or_tab, space_or_tab_min_max}
 use crate::event::{Content, Event, Kind, Link, Name};
 use crate::resolve::Name as ResolveName;
 use crate::state::{Name as StateName, State};
+use crate::subtokenize::Subresult;
 use crate::tokenizer::Tokenizer;
 use crate::util::constant::{HEADING_ATX_OPENING_FENCE_SIZE_MAX, TAB_SIZE};
-use alloc::vec;
+use alloc::{string::String, vec};
 
 /// Start of a heading (atx).
 ///
@@ -222,7 +223,7 @@ pub fn data(tokenizer: &mut Tokenizer) -> State {
 }
 
 /// Resolve heading (atx).
-pub fn resolve(tokenizer: &mut Tokenizer) {
+pub fn resolve(tokenizer: &mut Tokenizer) -> Result<Option<Subresult>, String> {
     let mut index = 0;
     let mut heading_inside = false;
     let mut data_start: Option<usize> = None;
@@ -281,4 +282,6 @@ pub fn resolve(tokenizer: &mut Tokenizer) {
 
         index += 1;
     }
+
+    Ok(None)
 }