GitLab

* src/xdisp.c (decode_mode_spec): Implement the %C construct.

* lisp/bindings.el (column-number-indicator-zero-based): New
defcustom.
(mode-line-position): Use %C when
column-number-indicator-zero-based is nil.

* src/xdisp.c (syms_of_xdisp) <frame-title-format>:
* src/buffer.c (syms_of_buffer) <mode-line-format>:
* doc/lispref/modes.texi (%-Constructs):
* doc/lispref/frames.texi (Frame Titles): Document the %C
construct.

* doc/emacs/display.texi (Optional Mode Line): Document
'column-number-indicator-zero-based'.

* etc/NEWS: Mention 'column-number-indicator-zero-based' and the
%C construct.