In reply to:

What official grammar? There isn't an official grammar. No-one has the power to make artificial rules, or to decide when a "rule" changes. The language is the language, that's all.

Well that's how I feel about language, too, but there's definitely an official language in terms of what is acceptable in a formal publication. If you turn in your doctoral dissertation using "they" to mean "he or she," or if it contains the word "ain't," or if it contains the sentence "Hamlet, Rosencrantz and Guildenstern were back at the crib kickin' it old-school," well you're going to get laughed out of the university.