VRR proxy is a Scheme object used for representing VRR
entities. Proxies are compared using the eq? command: if
p1 and p2 are proxies of the same entity, then
(eq? p1 p2) returns true. There are four kinds of proxies:
obj, go, anchor, and hanger,
and they are associated with the appropriate VRR
entities of the same
name. obj proxies are classified by their type. There are two
types of them: document and page. go proxies can
be classified by their type and subtype.