HTML doesn’t remove whitespace from quoted attribute values. XML replaces such things with a single space, but HTML leaves it intact. (If you want actual tabs a

HTML doesn’t remove whitespace from quoted attribute values. XML replaces such things with a single space, but HTML leaves it intact. (If you want actual tabs and newlines in XML or an HTML/XML polyglot—which can be reasonable, seen for example in the HTML title attribute—you have to encode them as and or similar.) So no, this does boil down to the behaviour quoted from the URL Standard.