What is meant by shell layer manager?

Shell layer manager is also called as shl in short. This utility is used for running number of scripts simultaneously at the same time in a single terminal. This utility plays a very important role in UNIX operating system because as we all know UNIX is a multi-programming operating system. So in other words there many be many instances or occurrences in which the users in the UNIX operating system use number of shells at the same time which are all to be managed and this management is done by the shell layer manager or shl. The prompt normally or generally used for denoting shell layer manager is >>>. In UNIX operating system the layers gets created by using shl using the shl command
create layername
Not only for creation of layer, there are many shl commands that are available in shell layer manager like to create a layer, remove a layer, and block a layer and so on using which the users can manage shell layers.