Regex for horizontal rules doesn't follow Markdown.pl and PHP Markdown

[jpfleury]

In Markdown, we can create a horizontal rule with 3 or more proper symbols (hyphens, underscores or asterisks) with 2 spaces maximum between each symbol. The following examples produce 3 horizontal rules with both Markdown.pl and PHP Markdown:

-  --  -

**  *  **

_  _  _

but Python Markdown doesn't create any horizontal rule:

<ul>
<li>--  -</li>
</ul>
<p><strong>  *  </strong></p>
<p>_  _  _</p>

For information, the regex that I use to highlight a horizontal rule in gedit is the following:

^[ ]{0,3}            # Maximum 3 spaces at the beginning of the line.
(
  (-+[ ]{0,2}){3,} | # 3 or more hyphens, with 2 spaces maximum between each hyphen.
  (_+[ ]{0,2}){3,} | # Idem, but with underscores.
  (\*+[ ]{0,2}){3,}  # Idem, but with asterisks.
)
[ \t]*$              # Optional trailing spaces or tabs.