I’ve been working on a small project, more of a web application than a site, that’s required the development of both a custom-theme and tightly coupled, but very specific functionality.
This is a very narrowly focused project (about which I’ll likely talk about at some point in the future) but in working on it, it’s forced me to get back into the theme development aspect of WordPress development a little bit.
No, I’m not doing any design – thankfully – but I am having to work on theme customizations from a functional perspective. In doing this, though, it’s had me revisit the required functions.php and some considerations I’ve never had before.
Furthermore, it’s caused me to look more deeply at the use of mu-plugins and ask when they are necessary and why I haven’t used them more in the past (or even when one would truly need to use them).
So I’m going to wax poetic about that a bit.
TL;DR
Functionality tied directly to the theme and WordPress core goes into functions.php. Domain-logic that required by the entire solution to work goes in a must-use plugin.
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