Enable VARIABLE to have frame-local bindings.
This does not create any frame-local bindings for VARIABLE,
it just makes them possible.
A frame-local binding is actually a frame parameter value.
If a frame F has a value for the frame parameter named VARIABLE,
that also acts as a frame-local binding for VARIABLE in F--
provided this function has been called to enable VARIABLE
to have frame-local bindings at all.
The only way to create a frame-local binding for VARIABLE in a frame
is to set the VARIABLE frame parameter of that frame. See
`modify-frame-parameters' for how to set frame parameters.
Note that since Emacs 23.1, variables cannot be both buffer-local and
frame-local any more (buffer-local bindings used to take precedence over frame-local bindings). (fn VARIABLE)