And this is a very, very interesting point of language. It makes it very hard at times to parse sentences--or even to explain how sentences should be parsed--because two words really function as one, which is difficult for some students to grasp.

'Crystal clear' having been collocated, really should function as a single word, as does the compound noun 'riding boots' or even, more understandable, 'mountain lion.' In diagramming a sentence, you wouldn't show lion as a noun and mountain as a modifier because the two words 'mountain lion' behave as one.

I wonder whether this is true for these collocated pairs, such as 'crystal clear'? Would 'crystal clear' function as one adjective if you were to diagram it in a sentence? Based on what I know about compound nouns, I would guess, yes. Does anyone here know exactly how these collocated pairs should be correctly diagrammed in sentences?

Anyway, thanks, wwh. Again, very interesting.