This one cracked me up!

Take this shit to Reddit

@Demolishun I think it's a requirement for programming languages to be Turing complete on their own.

That makes HTML 5 + CSS 3 a programming language, but HTML on its own isn't one.

@Demolishun It isn't defined anywhere, the main reason why I say this is that if a programming language doesn't need to be Turing complete then what's considered a computer also becomes uncertain. Eg. Is a bicycle transmission system a computer? It has input, output and a program consisting of two instructions, even if that program is limited to at most 6 combinations on your average city bike.

@Demolishun So this means that a computer is a device that can be instructed in some computational language, such that a machine that can only render html with no style isn't a computer. Yeah, this would make sense.
Now, the only problem is that no one will care because debating is more fun than deciding on sensible definitions.