Emphasis with `_`

[Eric Blair]

On 5/24/05, John Gruber <gruber at fedora.net> wrote:
> But even then we might be OK, if we say the rules for `_` emphasis are:
> 
> 1.  Opening emphasis is a `_` at word break position. In regex notation:
> 
>         \b_
> 
> 2.  Closing emphasis is a `_` followed by anything other than a
>     number or letter.
> 
> With these two rules, you could write something like this:

Actually, this would address an issue I hit a few days ago when I was
using reference style links. Here's the Markdown source (not bothering
with the references, but you all know what I mean):

> on [mach_inject][] and [mach_override][], but

and here's the XHTML that's generated:

> on <a href="http://rentzsch.com/mach_inject">mach<em>inject</a> and <a href="http://rentzsch.com/mach_override">mach</em>override</a>, but

As you can see, an <em> tag is opened inside the first <a> tag and is
closed in the second <a> tag.

--Eric