The q parameter has an inquestion operator that can take a question id.
Can it take multiple question ids?
My use-case is as follows:
I want to get an array of questions with their excerpts.
However, search/excerpts results don't include many of /questions properties (e.g., owner, view_count, bounty-related props, etc.), hence I'm forced to make >1 calls to get all desired properties.
If inquestion doesn't support multiple ids, I need to make 1 + n calls (1 to /questions, and n to search/exceprts, where n is the number of returned questions). But if it does, I would only need to make 2 calls.
No, it does not. It's the same operator as in the regular site search and that does not support multiple IDs either.
However, if you need the excerpt from a list of questions you already know the ID of, you can consider retrieving the body with the /questions call (by applying the correct filter) and stripping the HTML elements. That's pretty close to what the excerpt does.