Info-virtual-nodes is a variable defined in `info.el'.
Its value is

(("\\`\\*Index.*\\*\\'" (find-node . Info-virtual-index-find-node) (slow . t)) ("\\`\\*TOC\\*\\'" (find-node . Info-toc-find-node)))

List of definitions of virtual Info nodes.
Each element of the list has the format (NODENAME (OPERATION . HANDLER) ...)
where NODENAME is a regexp that matches a class of virtual Info node names.
It should be carefully chosen to not cause node name clashes with
existing node names. OPERATION is one of the following operation
symbols `find-node' that define what HANDLER function to call instead
of calling the default corresponding function to override it.