> What are the correct LaTeX commands? I think that these are exactly the
> commands which are correct from the TeX's point of view, aren't they?
They are as documented in the LaTeX manual plus documentation that
comes with the standard distribution. The example that gave rise to
this is an example of how they are not "anything TeX likes".
It would be difficult for us to make them anything else.
> I think that those parsers, if they want to be correct, *should* parse
> according to the general TeX syntax (and semantics).
No, not if they are parsing LaTeX documents.
You see TeX can have any syntax (in some sense of any:-) so a parser
that could do that would be as difficult to produce as TeX.
> [ But there is really only one correct parser---TeX ;-) ]
For TeX, yes (thankfully:-); but not for LaTeX documents.