Since PhpDocumentor allows Markdown in documentation blocks (as stated here), we have added Markdown support to PhpStorm 8 too when showing a quick documentation of classes, functions, etc. Here is a list of what is actually supported from Markdown syntax specification, with some examples:
Paragraphs separated by one or more line breaks. There is a continuous flow of text inside a paragraph without line breaks from the original description.
Headers. You can use the following style, for example:
My Header OR My Header
or use the number sign (#):
# My Header