I occasionally receive an error in the WordPress backend: "HTTP error." I'd like to troubleshoot myself, but first I want to know the source of the message. Is this a message generated by WordPress? Or has some other software (e.g. a plugin, my server OS, etc) generated the message? Either way, is there any official documentation regarding this error message? All I can find online is third party information on possible causes of the message--I can't find anything official.
There are many existing questions about "HTTP error" on this site:
but I have not found any that ask/answer my specific question.
To be clear, I'm not looking for tips on how to resolve the error. I would like to learn more about the error message, and as an initial step, I'd like to hunt down the official documentation on the error, if any. If I still need more assistance after, then I will consult one of the third party guides I have already found (many on this very site).