In Parameter§
See primary documentation in context for method capture.
method capture(Parameter:D: --> Bool:D)
Returns True for parameters that capture the rest of the argument list into a single Capture object.
sub how_many_extra_positionals($!, |capture) { capture.elems.say } how_many_extra_positionals(0, 1, 2, 3); # OUTPUT: «3» say &how_many_extra_positionals.signature.params[1].capture; # OUTPUT: «True»
Like raw parameters, Capture parameters do not force any context on the values bound to them, which is why their sigils are only used in declarations.