Clarify whose are constraints.
Clarify whose are constraints.

According to @moritz's comment in the IRC conversation pointed from
the issue. Closes #1217.

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