Overview
 About the Environment Editing Routines:
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 The Expand Library currently sports a number of functions that
 make playing around with the Environment strings possible. Great
 care has to be taken when doing so, as the functions perform unusual
 tasks. The XPenv???() have to be approached with care, the XPsetEnv()
 XPdelEnv() and XPreadEnv() functions, on the other hand, can be used without
 much prior knowledge.

 Undocumented features are used to achieve this, so no guarantee can be
 given that it'll work everywhere (although, to my knowledge, it does
 work, as DOS also uses the same methods currently).

 The XPenv???() functions alter the Original Copy of the environment
 strings. Every time one loads a copy of COMMAND.COM, a block with
 environment strings is supplied, which is what you see when you
 type "SET" at DOS. When a program is invoked, a copy of those
 strings is supplied to the program. The XPenv???() functions, however,
 alter the contents of the original strings. Changes are thus
 not visible when using Clipper's GetEnv(), but, they could be visible
 to programs executed from the Clipper Application (*). This feature thus
 makes it possible to change the PROMPT, the PATH or even add (or
 delete) some Environment variables for child processes.

 Note that the environment has a maximum size, which one can not exceed.
 Note also that changes made to the environment are also kept when
 the program terminates! Ensure yourself that you restore the
 original enviroment when QUITting..

 The XPenv???() perform quite 'Low level' Tasks. The other functions
 use the XPenv???() functions to do what they are intended to do.

 Again, please know what you're doing when playing with these functions..
 It might also seem quite difficult to implement it for your application,
 but have a look at XPDEMO.PRG, which quite well illustrates setting
 a different PROMPT for a Shell from Clipper, a feature much requested
 for Clipper applications.

 (*) You need to call a special function before running to ensure that.