drhowarddrfine - 7:29 pm on Mar 29, 2013 (gmt 0)
The SOLE purpose of a doctype for HTML is for Internet Explorer. Always has been. NO other browser ever required it and browsers changed their behavior to be compatible with IE's multitude of quirks and irresponsibilities.
XML did NOT abandon the DTD and true XML can still use custom DTDs.
The so-called "HTML5 doctype", as someone else said, notice there is no "5" in there. While it's allowed to use lowercase 'doctype' in this new version, uppercase was always required in the past and still works and validates with the new version.
Just rattling things off that I noticed and remembered.