Spoiler alert: no, they shouldn’t.
Yesterday, Marijn Haverbeke tweeted:
If you make accessibility or internationalization in a code library an optional component, you just know half of the people deploying it will ignore it—out of ignorance or as optimization. So taking the side of the end user versus the dev user means just pre-bundling these things
For very similar reasons, I refuse to make accessibility features configurable in my vanilla JS plugins.
Very much this. In short:
If you write a library, add accessibility features as standard.
If you fail to do this, you do a disservice to the developers who use your library and, worse, to the users of their software. Accessibility is for everybody, but it’s still surprisingly hard to get right: don’t make it any harder by neglecting to include it in your library’s design.
Make those accessibility features on-by-default.
You can’t rely on developers to follow your instructions to make the use of your library accessible. Even the most well-meaning developers find themselves hurried by deadlines and by less-well-meaning managers. Don’t even make accessibility a simple switch: just put it on to begin with.
Don’t provide a feature to disable accessibility features.
If you allow accessibility features to be turned off, developers will turn them off. They’ll do this for all kinds of reasons, like trying to get pixel-perfect accuracy with a design or to make a web application behave more like a “hip” mobile app. You’ll probably find that you can never fully prevent developers from breaking your accessibility tools, but you must make it so that doing so must be significantly more-effort than simply toggling a constant.