Don't use “custom DTDs”!
What's with the <blink>?
The W3C Style page contains a <blink> element. <blink> is not an HTML element and yet the page is valid according to some HTML validators. What's the trick?
In fact, the page is syntactically valid, because the element is declared in the document. As long as elements are properly declared, the page is valid in the SGML/XML sense.
But the page is not semantically valid. It is an SGML document, but it is not an HTML document. There is no official standard that defines what <blink> means.
The W3C Style page uses a non-standard element as a joke. If you know the history of CSS you may remember that one of the reasons for CSS was precisely to avoid that every browser invented its own non-standard elements, such as <blink>.
Don't use “custom DTDs”! What's with the
