
# Underline

With the flag `MD_FLAG_UNDERLINE`, MD4C sees underscore `_` rather as a mark
denoting an underlined span rather than an ordinary emphasis (or a strong
emphasis).

```````````````````````````````` example
_foo_
.
<p><u>foo</u></p>
.
--funderline
````````````````````````````````

In sequences of multiple underscores, each single one translates into an
underline span mark.

```````````````````````````````` example
___foo___
.
<p><u><u><u>foo</u></u></u></p>
.
--funderline
````````````````````````````````

Intra-word underscores are not recognized as underline marks:

```````````````````````````````` example
foo_bar_baz
.
<p>foo_bar_baz</p>
.
--funderline
````````````````````````````````

Also the parser follows the standard understanding when the underscore can
or cannot open or close a span. Therefore there is no underline in the following
example because no underline can be seen as a closing mark.

```````````````````````````````` example
_foo _bar
.
<p>_foo _bar</p>
.
--funderline
````````````````````````````````

An invalid intra-word delimiter run prevents an earlier run of the same length
from pairing with a later delimiter. Shorter intra-word runs remain literal
inside a valid underline span.

```````````````````````````````` example
__Test__Broken - because of a missing space after the closing "__" !!!

__foo_bar__
.
<p>__Test__Broken - because of a missing space after the closing &quot;__&quot; !!!</p>
<p><u><u>foo_bar</u></u></p>
.
--funderline
````````````````````````````````
