Mnemonics

"not!", "!nvert", "!mportant"

Used alone

! negated boolean coercer as in common parlance (that means "use it like you are used to doing")

Used as a brace pair or quote pair

Operators containing this character

! can mutate other operators to negate their boolean sense
!! is the second part of the ternary conditional operator
!!! is a fatal yadayadayada

When used inside regexes

Special Variables

As an adverb

:! before the adverb of an adverbial pair constructor, is shorthand for assigning a value of 0 (which is false)

Other Uses

! after a parameter in a prototype marks it as a required parameter
! as a class atrribute twigil designates it a "private attribute"
! as submethod parameter twigil creates an attributive parameter
! before a name in a "pair constructor"<> (and without a subsequent value) sets the key to a false value.
! designates a commandline option was prefixed with a + in a MAIN subroutine

Hyper operator and meta operator restrictions

Old, deprecated, or other language uses