Ideally, that kind of stuff should be in tag wikis. However, tag wikis aren't quite up to task yet. There's no way to link to a part of a tag wiki, so if you put too much stuff in them, it's difficult to locate the right section. And you can't close a question as a duplicate of a tag wiki.
So for questions like “What does this $language operator mean”, which are reasonable technical questions and whose only defect by Stack Exchange standards is that they are very broad (which would normally mean they should be closed as “not a real question”), I think a canonical reference question is a reasonable interim solution. I'm not a PHP guy, but I think the PHP examplePHP example is working well.
Since it's not expected that a single person would write and maintain the repository, I think community wiki is appropriate, as a sign that everyone is welcome to edit. Note that I do think the tag wiki rules, where edits are reviewed (except for users with 20k rep), would be more appropriate, but again, as an interim solution, I find this reasonable.
I think it would be better to have a very short question and a single answer containing the list of links, to respect the Q&A format. But it's not a big deal here.