$v is set with the content of the 0th element of the array that is the content of hash %pairs when keyed by the value $ca. If the content of the %types hash when keyed by the value $ca is true (non-zero), the operations assume that $v and $cv are numeric (otherwise assuming them to be strings). $v is given an empty value if it has not been previously defined, and $r is set to the result of a bitwise AND operation of itself and the result of the appropriate comparison, as selected by the value in $co.

HTH.