The following global symbols are defined by tcl++:
Tk_Window, useful for obtaining X information such as
colourmaps
error. Use error(char *format,...) to construct such
an object.
The format string is passed to sprintf, along with all remaining
arguments. The resulting string is what is return by the
error::what() method. Standard execptions are usually caught,
and the error message return by what() is attached to TCL's
error log, and TCL_ERROR return back to the interpreter.