QTextEdit markdown parser issue

[clarify]

I've discovered that when I nest font attributes, some can be missed.

For example this (produced by QTextEdit in Qt5) does not show strike-out when read by QTextEdit:

~~bold avec strike-out~~

But this works

bold avec strike-out

When reading markdown from the QTextEdit, the upper format is produced.

[clarify]

@clarify

This does not work: underline
i.e. the _ character causes italic not underline.