I agree with your intent, but in XML territory this is an incorrect use of "validate". That an XML document can be "parsed" -- that is, all the punctuation is correct, the tags are properly nested, etc. etc.-- is called "well-formedness". Validation is a much stronger constraint, that the document obeys the Document Type Definition (DTD) or perhaps some other schema, that specifies that in addition to well-formedness the document conforms about which elements and content may appear inside which other elements.
Browsers will certainly report bad syntax, but I don't know of any main line browsers which validate automatically. In any case, they could only do so if a DTD were included directly in the XML document or referenced by an external URL.
XML is a religion -- it's not a bad religion, but best not to anger the XML gods with <blasphemy satire="true">blasphemy</blasphemy>!