A set answers “what am I trying to do?”
Useful sets can focus on reframing a problem, expressing uncertainty, managing a discussion, explaining cause and effect, changing register or avoiding transfer traps. The organising principle is therefore functional rather than simply alphabetical or grammatical.
Grammar still appears inside the set, but it appears when it helps explain a decision. This keeps the learner close to language use instead of asking them to complete an entire grammar taxonomy before saying something useful.
Neighbouring Frames make the set educational
A set should not be a bag of phrases with the same keyword. Its Frames need a reason to live together: shared Move, recurring decision, register contrast or common learner problem. That relationship makes comparison possible.
Once several plausible Frames are nearby, practice can move from “do you understand this example?” to “which option fits this situation, and why?” That is where Contrasts and Choices become useful.
Sets are also navigation for a large corpus
Metkagram contains a large pattern catalogue, so sets provide human-scale entry points. A learner can choose one job, work through a bounded group, then follow related Frames or a Route instead of scrolling through thousands of records.
The design goal is not to hide the size of the corpus. It is to make size usable. A large library without strong grouping becomes search infrastructure; a set turns part of that library into a lesson-shaped object.