On Unix&Linux, I am used that questions that have a restrictive tag should only be answered with that restriction in mind, or with a generic answer which encompasses the restriction.
As an example, someone asks: "how do I install Calibre with my package manager" and tags it with ubuntu.
In that case an answer that includes the Centos installation program
yum is not appropriate, but one using
apt-get (the one used on Ubuntu) is. The word Ubuntu does not have to appear in the question¹.
After answering "How can I extract some chapters or sections from an ebook into a new one?"—that doesn't mention any particular ebook format in the text of the question—I answered how to do that for PDF and DjVu.
The OP had already answered himself for EPUB, and I realised later that there was an epub tag on the question. Had I seen this before, I would not have answered for PDF or DjVu ebook file formats, but since the answer was there, and even had an upvote (in addition to a downvote), I thought I ask what the OP had intended, before deciding to delete my answer as inappropriate.
The OP indicated that non-EPUB answers were OK, and in the ensuing comment exchange I pointed out the help on tags. It says:
A tag is a word or phrase that describes the topic of the question. Tags are a means of connecting experts with questions they will be able to answer by sorting questions into specific, well-defined categories.
The help text doesn't mention answers at all, but the OP pointed out that on other SE sites this might be differently interpreted and on meta.stackoverflow.com there seems no definitive support for my, or the OP's reading either.
I am not looking here to be right or wrong, I just would like to use meta.ebooks to discuss this point, so we have a clear reference on how we want this to be handled on this site. This allows us (after the discussion) to (re-)tag consistently if necessary.
As far as I am concerned there is something to say for both approaches, but mixing them on one site is going to be confusing.
¹ You will quickly get downvoted on U&L if your answer does not apply because you overlooked a tag