Where X is any ASCII char chosen by the user. An argument is only
interpreted as custom-quoted if it starts with '!' and the line doesn't
end right after it. Custom quotes don't interpret backslash-escape.
This change only affects command arguments which mpv parses (not array
commands), and not tokens before the arguments (where applicable - key
name, input section, command prefixes, command name).
Avi Halachmi (:avih)
4f129a3eca