Word counts to stay within makes no sense to me. Am I dealing with an idiom here? Because if I am, I would like to know which that idiom is. Hard as I tried, I could find no such idiom anywhere I could look it up in.
Word counts to stay within is an example of a construction called a Relative Infinitive.
That means it's a relative clause, but instead of being a tensed relative clause, it's an infinitive.
Relative infinitives can be converted to tensed relative claues, but they always have some deontic modal involved (like must, should, have to, ought to).
- the man to do the job = the man that/who should do the job
- the man to see = the man that/who one ought to see
- the rope to pull on = the rope that/which one has to pull on
- page limits to stay within = page limits that/which one must stay within
It's a sneaky way to put a modal meaning into a sentence without actually using a modal.
To me more than an idiom, that sounds like a perfect sentence.
While the context could have helped more, however my interpretation of this sentence is - "It is frustrating when I have a word limitation to stick to."
This means that the speaker is talking about a situation wherein he is supposed to limit his expression (either in written or oral) within a specific count of words. He may have more to say / write but the word limit restriction is not allowing him to do so.
I would word it as 'it's frustrating when I have to stay within the word count/limit.'
It is ambiguous to me. "Word counts to stay within" could express a minimum, a maximum, or a range.