Looking for library of functions

Can anyone please point me to a set of good functions to search and manipulate HTML? Mainly I'm looking to buffer HTML that is output by another script and fix some issues with it. Such as missing " around property values and many other things. Function examples: Find tags in HTML, replace tags, modify tags, find properties in tags, return entire HTML elements such as tables even if there are nested tables; meaning if I have: <table class="someclass"> <tr><td> <table><tr><td></td></tr></table> </td></tr> </table> It should be able to return the entire table containing the other table. Sorry if I'm not explaining this well. Thanks! Shawn