The definition of a user-defined class, held in the interpreter’s class
registry (not as a Value — variables hold a lightweight Value::Class
handle that names this entry).
Backing data for Value::DefaultDict — the entries + the missing-key
factory. Stored behind a Box on the DefaultDict variant so the
inline Value enum slot stays narrow.
A regex match: its capture groups (index 0 is the whole match) plus a
name→index map for named groups. Offsets are character indices, matching
Python’s str-based re.
Backing data for Value::Partial — the bound callable + its
captured positional / keyword args. Stored behind a Box on the
Partial variant so the inline Value enum slot stays narrow.