Underlined headers displayed incorrectly

[pierreporte]

The level 1 and 2 titles, when created using an underlining row of = or -, are not displayed correctly. The actual text of the title remains in the common style and is not enlarged. Below is a screenshot.

[brrd]

Actually this issue is difficult to fix properly because of CodeMirror parser design (it goes line after line and can not go back to a previous line). In my opinion, this syntax is a tricky feature of markdown which should be avoided whenever possible because it's much harder to handle than the classical # expression (regardless of the parsing system). But I agree that it is important to provide support for it.

Abricotine already supports this syntax in the table of content (here). We need a new method independent of CodeMirror's parser to parse the content and correct this on editor change.

[brrd]

Related feature request in CodeMirror: codemirror/codemirror5#839

A workaround here: codemirror/codemirror5#2143 (comment) (but we must check performance on large documents).

[brrd]

CodeMirror 5.27.0 now features a new StringStream.lookahead method which can help fixing this. IMO the best solution would be to fix the markdown mode directly into CodeMirror.