I am new to jQuery, but came across an issue in the clear: function.

Where jQuery trim whitespace it trims and lower-cases the entire arg where it looks like it only needs to lower-case the html tags. We just removed the jQuery.trim(arg).toLowerCase(),... to jQuery.trim(arg),... but I think it is safer to lower-case the tags. Maybe just lower case within side the tags.

var s = jQuery.trim(arg).replace(/<.*?>/g, "$0"), div = doc.createElement("div"), tb = [];

instead of

var s = jQuery.trim(arg).toLowerCase(), div = doc.createElement("div"), tb = [];

or something of that affect without removing the .toLowerCase() function.