Coming at this cold, this stuff is way beyond me, but there do seem to be quite a few references to "first and follow sets" on pages that relate to predictive parsing. I couldn't tell you if this is right or not, as I've skimmed quite a few of these pages but can't even begin to understand what they're talking about. I guest this relates to why I still have trouble with the RegEx features in Trados Studio :) Hopefully, it might put you on the right track though. Suerte.

Here's one example, though there are plenty available if you run a search for predictive parsing "first and follow":

The construction of a predictive parser is aided by two functions associated with a grammar G. These functions, FIRST and FOLLOW, allow us to fill in the entries of a predictive parsing table for G, whenever possible.
https://www.cs.uaf.edu/~cs331/notes/FirstFollow.pdf