What exactly is Zend's relationship to PHP? I don't mean the framework but the company itself. Are they the gatekeepers or guardians of sort?
I've just been reading up on PHP, and other than requiring knowledge of C to extend it you apparently need to learn the Zend APIs. But when you first start out with PHP you don't need to know anything "Zend", and the same goes for non-Zend frameworks like Cake and CodeIgniter.
So I'm confused and curious about when knowing things Zend begins to matter in using PHP.