int referencep(&ref)
mixed ref

Returns true if ref is a reference. Note that there has to be a leading &.
References behave just like other local variables but if their value is
changed the associated variable in the calling functions is changed, too.
referencep() gives no information about the actual type of the variable.

See also clonep, stringp, objectp, pointerp, floatp, mappingp.
