This is a major upgrade, and requires some significant compatibility
work:
* Migrating the pattern-removal logic to use the Registry feature.
* Handling the removal of positional arguments in markdown extensions.
* Handling the removal of safe mode.
Our nested code block processor wasn't using the correct test for
whether a paragraph was empty of other content; first, we need to
confirm no children, and second, we need to confirm there is no text
before/after the code block element inside the p tag.
This commit adds a Markdown tree-processor extension that renders
multi-line code blocks that are nested inside lists with the
formatting. Note that the code block could be nested inside multiple
list levels and would still get rendered correctly.
Tim: This fixes the need for unpleasant workarounds like
f5bfa4e793 and makes nested code blocks
in our documentation look exactly how users would expect them to.