Deep equality against a literal. For enums, ids, booleans, numbers.
The value is a string with non-whitespace content. The weakest useful check.
Case-insensitive substring. For free text where a keyword must appear.
Membership in a fixed set. For value-list parameters.
A regular expression, supplied as a string with optional flags.
Numeric bound, either end optional.
The value's JSON type. For asserting shape without asserting content.
The parameter must be absent or null — for asserting a default was left alone.
One check against one parameter value.