[php-langspec][Issue #226] - Should `$a instanceof $b instanceof $c` be permitted in implementation/specification?

You can view the Issue on github:
https://github.com/php/php-langspec/issues/226

Comment by nikic:
Nice catch! I don't think that allowing this was intentional. The operator is marked non-associative in the PHP grammar, but because it's not an ordinary binary operator (with expressions on both sides), that does not end up actually mattering.

If we want to change this, then an issue should also be filed on bugs.php.net, as changes generally always go from the implementation to the spec, no the other way around. I also suspect that this is going to be ugly to fix.