Learn English – What do you call a note that gives preliminary information before the main part

I'm looking for a single word (if not, a natural phrase) for a note that you write before starting the main article/part/question etc.

It can give preliminary information (in general). However, it can be a mild warning (but I would like to avoid calling it a "warning" which is too strong) or a reminder (thus, we can call it a "reminder" but I want a more general word).

An example context would be, when you are posting a question on stackexchange sites, you put a note in advance that people read it before the question and you make them think twice before posting an answer, you remind them that the question is (not) about this or that etc.

For example:

_____: This question is not only about finding a single word. I would like to get a detailed answer that addresses all the related questions.

<< Main question… >>

I considered the word note itself but I want to distinguish it from the notes that you write after or during the main part.

Then, advance note¹ came to my mind as a phrase but it also has another meaning and can be confused with advance notice.

Prenote² could be a nice word but it does not sound that natural and dictionaries list it as a verb only.

There are of course words like preface and prologue but they are usually too formal and comes before longer written works like novels.

Caveat³ is similar to warning but it might give special instructions. Can it be the word I'm looking for? I might have seen it used in this way on EL&U but it is used in law also.

_{I might be over-thinking and the answer might be very simple but I wanted to give as much information as I can. You might also talk about differences between words that fit to similar settings.}

_{¹ a draft on owners or agents of a ship drawn by the master for the benefit of a sailor usually for one month's advance wages [MW]}

_{² trans. To note or mention previously. [OED]}

_{³ an explanation or warning that should be remembered when you are doing or thinking about something [MW]}