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