Variable: line-prefix
line-prefix is a buffer-local variable defined in xdisp.c.
Documentation
Prefix prepended to all non-continuation lines at display time.
The value may be a string, an image, or a stretch-glyph; it is
interpreted in the same way as the value of a display text property.
This variable is overridden by any line-prefix text or overlay
property.
To add a prefix to continuation lines, use wrap-prefix.
Probably introduced at or before Emacs version 23.1.
Source Code
// Defined in /usr/src/emacs/src/xdisp.c
DEFVAR_LISP ("line-prefix", Vline_prefix,
doc: /* Prefix prepended to all non-continuation lines at display time.
The value may be a string, an image, or a stretch-glyph; it is
interpreted in the same way as the value of a `display' text property.
This variable is overridden by any `line-prefix' text or overlay
property.
To add a prefix to continuation lines, use `wrap-prefix'. */);