A lot of use cases for the progress functions require clamping the value to 0-100%. Some use cases don't... but the driving use cases generally do.

Should progress() clamp to 0-100% by default? It's always possible to get the unclamped result by using calc().

If it doesn't, then authors will need to manually clamp it all the time, which probably gets annoying, especially since you need to repeat the start/end values. clamp(0%, progress(_value_, 0%, 100%), 100%)...