[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 mattacosta:
I think a better solution is to just note that the Zend implementation is non-conforming. This has the benefit of keeping the parse error as acceptable, while also letting other parsers choose if they want to implement the deviation for compatibility purposes.

Since there are already multiple implementations that do not have bug, it makes more sense to go through the RFC process at this point rather than unilaterally make them in violation of the specification too.