firebug returns syntax error in doctype?

Question

Why does Firebug return an error in my doctype?

Answer 1

DOCTYPE normally is expressed on one line like below. and can cause syntax error

But even sometimes it will yell about a syntax error when a src attribute is not declared for an element. Firebug can also through this error when a source is not found or is called twice on one page. EX: script/image/link.