Create and return a twin copy of the current buffer.
Unlike an indirect buffer, the new buffer can be edited
independently of the old one (if it is not read-only).
NEWNAME is the name of the new buffer. It may be modified by
adding or incrementing
unique buffer name. If nil, it defaults to the name of the
current buffer, with the proper suffix. If DISPLAY-FLAG is
non-nil, the new buffer is shown with `pop-to-buffer'. Trying to
clone a file-visiting buffer, or a buffer whose major mode symbol
has a non-nil `no-clone' property, results in an error.
Interactively, DISPLAY-FLAG is t and NEWNAME is the name of the
current buffer with appropriate suffix. However, if a prefix
argument is given, then the command prompts for NEWNAME in the
This runs the normal hook `clone-buffer-hook' in the new buffer after it has been set up properly in other respects.