Which Function mode is a minor mode that displays the current function name in the mode line, as you move around in a buffer.
To enable (or disable) Which Function mode, use the command M-x
which-function-mode. This command is global; it applies to all
buffers, both existing ones and those yet to be created. However, this
only affects certain major modes, those listed in the value of
which-func-modes. (If the value is
t, then Which Function
mode applies to all major modes that know how to support it--which are
the major modes that support Imenu.)
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