I have a document which is almost valid HTML (with the HTML 4 transitional doctype), the only warnings I'm currently getting are about ampersands in query strings.
When I try $('.classname') in every browser I get the object expected, in IE 6 & 7 I get null, I've also tried $('#someId') and get the same issue (and document.getElementById('someId') works fine in IE). Am I going crazy or is there something I'm missing?