tclPkgSetup is the support/utility command that enables -lazy in package index script. It's defined package.tcl, which is part of the standard Tcl distribution.
tclPkgSetup is deprecated. According to DGP ,irc #tcl channel, 2012-12-03, it's abut three layers of bad ideas deep. For backwards compatibility, it will probably remain available for some time.
This is a utility procedure use by pkgIndex.tcl files. It is invoked as part of a "package ifneeded" script. It calls "package provide" to indicate that a package is available, then sets entries in the auto_index array so that the package's files will be auto-loaded when the commands are used.
Arguments: