Note that this feature is intended for administrators or advanced users only and normally there is no need to use it. However, it could help in some unusual situations like system recovery tasks when another terminal is not available.
On systems which support the job control, the running command (a so-called process group) can be stopped (suspended) with the ctrl-Z key and then it can be placed in the background (i.e running without the terminal I/O) while other commands can be normally started in the foreground.
CLEX does not support full job control. It can only resume (restart) the command suspended with ctrl-Z, but a shell session can be started before resuming the command. In this shell session virtually any tasks can be performed.
clex --version