The qualified name of this safe tcl command is ::safe::loadTk.
The documentation can be found at http://www.tcl.tk/man/tcl/TkCmd/loadTk.htm .
The -use option forces the subordinate slave interpreter's main window to be a child of (i.e., embedded within) the X11 window whose ID is windowId. The -display option forces the subordinate slave interpreter's main window to be on the given X11 display called displayName.