There should be a drop-down/running list of matching suggestions available with at least the special field markers when selecting a citation key pattern.
This should reflect in both library properties as well as preferences.
The matching will involve search (filtering, to be more precise), so the list of available special field markers should be populated and kept somewhere (if not already done - as far as I am aware, we do only a case-by-case matching with the input pattern string^[1], and the generator fails without warning if no pattern matches^[2] - no citation key is generated^[3]).

This will enhance UX greatly, as it will take away some load to read the documentation again if a user forgets the pattern marker, and also bring in some convenience for not having to press the enter key every time (as in, the click for selecting a sugegstion/drop-down item should be enough).

Some more context:

• ^[1] One can find the patterns in BracketedPattern.java
• ^[2] In case of a single field marker. In case of compound patterns consisting of a combination of field markers, any one of them being invalid renders only THAT part invalid. The citation key is then partially generated as per the valid components only. E.g. [auth]_[yger] can generate Corti_ as a key instead of Corti_2011.
• ^[3] Ideally, there should be a warning notification in that case - either while pressing enter after providing such a pattern, or on trying to generate a citation key using it (on empty string), or preferably both.