Explains sinkage of maps, closes #1718
Explains sinkage of maps, closes #1718

dmaestro/doc,jonathanstowe/doc,jonathanstowe/doc,dmaestro/doc,jonathanstowe/doc,perl6/doc,perl6/doc,MasterDuke17/doc,dmaestro/doc,stmuk/doc,tbrowder/doc,dmaestro/doc,perl6/doc,tbrowder/doc,tbrowder/doc,MasterDuke17/doc,tbrowder/doc,dmaestro/doc,perl6/doc,stmuk/doc,jonathanstowe/doc,stmuk/doc,MasterDuke17/doc,stmuk/doc,stmuk/doc,MasterDuke17/doc,perl6/doc,jonathanstowe/doc