Currently it's possible to format text with <del> by using the syntax ~~foobar~~:
foobar. This is quite useful for representing removed text and inline diffs. However, it should also be possible to format text with the reciprocal element, <ins> (to represent inserted text). This is particularly relevant for a markup language meant to be used in a code review context.
Markup for this could be e.g. ++foobar++, which is currently unused: ++foobar++.