PR 25466 makes the tokenizer emitting a deprecation warning if the numeric literal is followed by one of keywords which are valid after numeric literals. In future releases it will be changed to syntax warning, and finally to syntax error.

It is breaking change, because it makes invalid currently allowed syntax like `0 in x` or `1or x` (but `0or x` is already error).

See also issue21642 which allowed parsing "1else" as "1 else". Not all were agreed with that fix.

Perhaps we need to rewrite also some paragraphs in the language specification.