If buffers being compared are narrowed at the time of invocation of
ediff-buffers will preserve the narrowing range. However,
ediff-files is invoked on the files visited by these buffers,
that would widen the buffers, since this command is defined to compare the
the corresponding ‘-wordwise’ commands, narrows the variants to the
particular regions being compared. The original accessible ranges are
restored when you quit Ediff. During the command, you can toggle this
narrowing on and off with the % command.
These two variables control this narrowing behavior:
t, Ediff narrows the display to the appropriate range when it is invoked with an ‘ediff-regions...’ or ‘ediff-windows...’ command. If
nil, these commands do not automatically narrow, but you can still toggle narrowing on and off by typing %.