Markdown attribute support

[kirkilj]

From the DITA-OT docs, I can see that ids and class names can be included within curly braces for some Markdown structures.

1. Can someone provide a link to the most authoritative specification of which Markdown structures can have attributes applied to them in the version of Markdown that LW-DITA supports?
2. Are custom attributes supported, such as {lang=fr} or {data-toggle=modal} or conditional attributes such as {audience=internal}?