:method and :multi

[benabik]

When working my way through PAST::Compiler, I found a lot of code of this format:

=item as_past(TYPE)

.sub 'as_past' :method :multi(_, TYPE)
    .param pmc node
    .param options :slurpy :named

PDD 19 (PIR) mentions :multi, and directs the reader to PDD 27 (Multiple Dispatch) which only mentions :multi in passing.

Consensus on #parrot at the time (whiteknight and tcurtis) was that the first argument to :multi here was the method invocant. This is unexpected enough to deserve a mention in the docs.

[benabik]

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