Add note on where-clause side-effects
Add note on where-clause side-effects

https://rt.perl.org/Ticket/Display.html?id=130886
stmuk/doc,MasterDuke17/doc,MasterDuke17/doc,tbrowder/doc,jonathanstowe/doc,MasterDuke17/doc,jonathanstowe/doc,dmaestro/doc,antquinonez/doc,jonathanstowe/doc,perl6/doc,gfldex/doc,gfldex/doc,perl6/doc,antquinonez/doc,antquinonez/doc,gfldex/doc,dmaestro/doc,perl6/doc,tbrowder/doc,jonathanstowe/doc,perl6/doc,gfldex/doc,dmaestro/doc,antquinonez/doc,tbrowder/doc,dmaestro/doc,tbrowder/doc,stmuk/doc,perl6/doc,dmaestro/doc,stmuk/doc,stmuk/doc,stmuk/doc,jonathanstowe/doc,MasterDuke17/doc,gfldex/doc,antquinonez/doc