":localpart" / ":domain" / ":all"
Addresses are one of the most frequent things represented as strings. These are structured, and being able to compare against the local- part or the domain of an address is useful, so some tests that act exclusively on addresses take an additional optional argument that specifies what the test acts on.
These optional arguments are ":localpart", ":domain", and ":all", which act on the local-part (left-side), the domain part (right- side), and the whole address.
The kind of comparison done, such as whether or not the test done is case-insensitive, is specified as a comparator argument to the test.
If an optional address-part is omitted, the default is ":all".
It is an error to give more than one of these arguments to a given command.
Core : Requires no import statement