kitty/docs/underlines.rst
2022-01-18 12:13:51 +01:00

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Colored and styled underlines
================================
|kitty| supports colored and styled (wavy) underlines. This is of particular
use in terminal editors such as vim and emacs to display red, wavy underlines
under mis-spelled words and/or syntax errors. This is done by re-purposing some
SGR escape codes that are not used in modern terminals (`CSI codes
<https://en.wikipedia.org/wiki/ANSI_escape_code#CSI_(Control_Sequence_Introducer)_sequences>`_)
To set the underline style::
<ESC>[4:0m # this is no underline
<ESC>[4:1m # this is a straight underline
<ESC>[4:2m # this is a double underline
<ESC>[4:3m # this is a curly underline
<ESC>[4:4m # this is a dotted underline
<ESC>[4:5m # this is a dashed underline
<ESC>[4m # this is a straight underline (for backwards compat)
<ESC>[24m # this is no underline (for backwards compat)
To set the underline color (this is reserved and as far as I can tell not actually used for anything)::
<ESC>[58...m
This works exactly like the codes ``38, 48`` that are used to set foreground and
background color respectively.
To reset the underline color (also previously reserved and unused)::
<ESC>[59m
The underline color must remain the same under reverse video, if it has a
color, if not, it should follow the foreground color.
To detect support for this feature in a terminal emulator, query the terminfo database
for the ``Su`` boolean capability.