I think you've missed the point of that completely. It's for use in aliases to check whether they were called from the Command Box, (notice that the command box is
not the editbox).
eg.
cmdecho {
;Here's an alias that uses $cmdbox
if ($cmdbox) echo -a This is a special echo that only works from the command box. $1-
}
Now try that alias in the regular editbox and nothing happens. But use it from the
actual command box and it'll work (Use Alt+Q to toggle the command box on/off).