Underline XWiki syntax

This is not __ underlined __  => This is not __ underlined __
This is not __underlined __  => This is not __underlined __
This is not __ underlined__  => This is not __ underlined__
This is __underlined__ => This is <em class="underline">underlined</em>
This is __a__ letter underlined => This is <em class="underline">a</em> letter underlined
This is __a__ short underline__ => This is <em class="underline">a</em> short underline__
This is __all __ underlined__ => This is <em class="underline">all __ underlined</em>
This is __all __underlined__ => This is <em class="underline">all __underlined</em>
This is __one__underlined__ => This is <em class="underline">one</em>underlined__
__a__ => <em class="underline">a</em>
More __underlines__ on a __line__ => More <em class="underline">underlines</em> on a <em class="underline">line</em>
The extra lines are ____inside___ => The extra lines are <em class="underline">__inside_</em>
This__is__underlined => This<em class="underline">is</em>underlined
__Eeny__meeny__miny__moe__ => <em class="underline">Eeny</em>meeny<em class="underline">miny</em>moe__
__ Eeny__meeny__miny__moe__ => __ Eeny<em class="underline">meeny</em>miny<em class="underline">moe</em>
this is an underlined ______ text => this is an underlined <em class="underline">__</em> text
Ignore __things__ inside <script> a__i = 0; m = a__i; </script> => Ignore <em class="underline">things</em> inside <script> a__i = 0; m = a__i; </script>
Ignore <a href="/some__page__with__underlines">attributes</a> => Ignore <a href="/some__page__with__underlines">attributes</a>

Multiline examples:
This is __not
underlined__
 => 
This is __not
underlined__

<script>
m = a__i; n = a__i;
</script>
m = a__i; n = a__i;
 =>
<script>
m = a__i; n = a__i;
</script>
m = a<em class="underline">i; n = a</em>i;