what is sub-makefile and when it is used?

Hi,

In Tcl, Makefile.PL reads:

    # This is to allow propagation of this value to sub-Makefile.PLs
    $ENV{'TCLSH_PROG'} = $tclsh;

Going to get rid of this;

Does Tkx somehow depend on this?

Same thing for these lines in Tcl::Tk's Makefile.PL :

# Allow the tclsh prog to be provided by env var or arg
if ($tclshArg) {
    $tclsh = $tclshArg;
} elsif (defined($ENV{'TCLSH_PROG'})) {
    $tclsh = $ENV{'TCLSH_PROG'};
}

Going to get rid of this as well; who use this?

TIA, 
Vadim