To clarify a few points: this isn't using the Perl/Tk module; this is instead using a wrapper to use Tcl/Tk instead. Tcl::pTk is pure Perl, and likely so is IB2017's program. The C bindings to Tcl/Tk are all contained in Tcl.pm. Also, recent ActiveTcl only provides Tk for Aqua, so there's no use of XQuartz in this case. The Perl/Tk module however only works with XQuartz, as it has not been updated to work on Aqua.