I'm working on fulfilling a feature request for my package ten-hundred-mode - specifically, that it provide a "permissive" option where it merely highlights impermissible words, rather than immediately removing them in the fashion of Cleartext. I thought Flycheck would be a good method of doing this highlighting, and indeed it didn't take much effort to write a checker. But then I ran into some trouble.
Specifically, it is not clear to me that a method exists of enabling this checker while not affecting whatever other checkers the user currently has active. That's important because I want to fulfill the same use case as
flyspell-prog-mode, and provide a minor mode which can identify and operate on only comments, strings, and docstrings in source code. To do that with a Flycheck checker, I need to be able to activate it without in any way modifying whatever collection of checkers, or none, the user has configured for herself.
I can see several ways of activating my checker when someone activates my minor mode. I haven't been able to find one which I'm certain will do so without potentially breaking the user's configuration. No doubt many people here know more than I do about Flycheck's internals. (That's not a high bar to clear.) If a way exists, perhaps such a person will point me in its direction.