[Attribute names](http://www.w3.org/TR/2011/WD-html5-20110525/syntax.html#syntax-attribute-name) can contain most unicode characters for html5. Why this level of filtering them down? Is it because of the DOM throwing an error because of it's own internal restriction?

Can you document, in a comment before the if, what's going on and what this range represents in relation to that.