php language grammar

hi everyone, i have to write work abaut "formal gramatic in language php". As i understand it is the way as compiler works. e.g. if i write "function", then php compiler looks for funcion name, then for "(" and so on.. so i was wondering if there are written down all those rules.. i think theese things should be documented, because if developers add new function, it should be documented somewhere somehow not just in the code. is there any info about that? thanx in advice p.s. sorry for my english:)