What does this and other similar IE code lines mean in an HTML5 do
As @FDL pointed out, use a conditional stylesheet if you've got a moderate amount of styles to apply various versions of IE.
For minimal positioning tweaks, I use html classes (like ie8 or ie9) and just drop the modifications into my master stylesheet.
For example:
.filter-bar .item { float: left; vertical-align: top; }
.ie8 .filter-bar .item { position: relative; top: 2px; } /* fix a gap in IE8 */