Concatenation and the standard

According to this page "A ## operator between any two successive identifiers in the replacement-list runs parameter replacement on the two identifiers". That is, the preprocessor operator ## acts on identifiers. Microsoft's page says ", each occurrence of the token-pasting operator in token-string is removed, and the tokens preceding and following it are concatenated". That is, the preprocessor operator ## acts on tokens.

I have looked for a definition of an identifier and/or token and the most I have found is this link: "An identifier is an arbitrary long sequence of digits, underscores, lowercase and uppercase Latin letters, and Unicode characters. A valid identifier must begin with a non-digit character".

According to that definition, the following macro should not work (on two accounts):

#define PROB1(x) x##0000
#define PROB2(x,y) x##y
int PROB1(z) = PROB2( 1, 2 * 3 );

Does the standard have some rigorous definitions regarding ## and the objects it acts on? Or, is it mostly 'try and see if it works' (a.k.a. implementation defined)?