Hopefully someone can write a bit comparing and contrasting the
use of this variable and [TCLLIBPATH], and the Tcl variable $[auto_path],
describing to the developer when each should and should not be used,
and to the user of Tcl applications just when each are safe or not safe to 
set.

Another useful thing to document here is what the format for
the value should be.  Is this a colon seperated series of
directories, a space seperated list of directories, or some
kind of list of paths to pkgindex.tcl files, or just a single
path?

See also [magic names].
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