Indeed, and also Joomla. But the thing with all of these CMS systems is that they're already written. So the related "PHP work" is writing or tweaking plugins

Indeed, and also Joomla. But the thing with all of these CMS systems is that they're already written. So the related "PHP work" is writing or tweaking plugins for them. It's kind of like acknowledging the footprint of Microsoft Excel and VBA. Yes, it's quietly a huge deal, and thousands of people hold a job largely because they maintain it for an organization. But it's also the sort of thing one "stumbles into". They don't get hired specifically for that, and it doesn't really transfer to more general developer jobs.