Documentation for infix :
Documentation for infix :, assembled from the following types:
Used as an argument separator just like infix
, and marks the argument to its left as the invocant. That turns what would otherwise be a function call into a method call.
substr('abc': 1); # same as 'abc'.substr(1)
: is only allowed after the first argument of a non-method call. In other positions it's a syntax error.