Since: Version 20201031-154415-9614e117
The functionality described in this section requires version 20201031-154415-9614e117 of wezterm, or a more recent version.
Splits the current pane in half horizontally such that the current pane becomes the left half and the new right half spawns a new command.
SplitHorizontal requires a SpawnCommand parameter to
specify what should be spawned into the new split.
See also: SplitPane.