So far, I have implemented the following extensions:
- abbreviations
- auto identifiers and auto link (similar to pandoc)
- css bootstrap (to output some classes specific to bootstrap for some elements)
- custom containers (mostly block
:::and inline::) - definition lists
- Emojy/Emoticons
- Emphasis extra (strikethrough, subscript, superscript, inserted, marked)
- Figures (as described here)
- Footnotes
- Special/Attached attributes (allows to attach css attributes to the current block or the previous inlines with the syntax
{...}), works with all blocks and all inlines, including headings, fencedblocks - Softline as Hardline
- Lettered list (a. b., A. B., i, ii. iv, …etc.)
- Mathematics (block/inline escape
$$...$$, and$...$) - Medias (renders differently image with url that have a mime/type that is a video or music, or links to youtube/vimeo)
- Smartypants
- Pipe tables
- Grid tables (slightly extended version of pandoc)
No real issues. Maybe attached attributes are a bit specials, as they need to have hooks for some other block parsers (like fenced code blocks, to parse the attributes before parsing the info string, or for headings before removing the optional trailings ###).
In terms of performance, the side effect of adding proper extensibility for all these extensions (including the ability to remove/modify standard CommonMark parsing) has slow down the whole by around 20% (in C#), which is quite acceptable.