After some research I had begun to start to name all my html divs using hyphens because I read that method carried the most benefits (Naming "class" and "id" HTML attributes - dashes vs. underlines). Now I realized why I was using underscores before and that's because rails uses them!
For example:
<%= select('test', 'foo', ........)
will generate
<select id="test_foo"........>
omitting 'test'
gives
<select id="_foo".............>
as we can see, rails uses underscores when automatically prefixing/concatenating HTML ids. I was wondering why rails uses the underscore instead of a hyphen and if there's anyway to change this? Thank You!