type test0 = A.Contains<'a' | 'b', 'b'> // False
type test1 = A.Contains<'a', 'a' | 'b'> // True
type test2 = A.Contains<{a: string}, {a: string, b: number}> // False
type test3 = A.Contains<{a: string, b: number}, {a: string}> // True
type test4 = A.Contains<never, never> // False
/// Nothing cannot contain nothing, use `A.Equals`
Check whether
A1is part ofA2or not. It works like Extends but Boolean results are narrowed to [[False]].