All support types can be part of a union, with the following caveats: *%void%* can't be part of a union type *%?Class%* is equivalent to *%Class|null%* *%false%* is an addition, as it is used in the PHP standard library
e.g.: %*strpos() : int|false%* No redundant types, such as: *%bool|false%*, or: *%object|Whisky%* Variance: Union types follow standard variance rules Order is irrelevant: *%int|string%* and *%string|int%* %*array|Traversable*% is the same as %*iterable*%