Tells a set from a value that merely starts with a brace

All 9 scenarios hold

These rules cover one cell value: strings, quoting, the three collection forms, and the errors a malformed value raises. The three collection forms are a list, a set, and a map.

This table holds two outcomes, as the table for a list does. A value that does not open a set captures as a plain string. A value that opens a set and does not complete it fails to parse.