If non-nil, SPC in a menu visits subnodes.
If this is non-nil, and you scroll far enough in a node that its menu
appears on the screen, the next SPC
moves to a subnode indicated by the following menu item. This means
that you visit a subnode before getting to the end of the menu.
Setting this option to nil results in behavior similar to the stand-alone
Info reader program, which visits the first subnode from the menu only
when you hit the end of the current node.