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Detail:
  When this module is installed, it intercepts Wimp service calls in order
  to add an extra button (labelled "Debug") to Wimp error boxes where either
  (a) the top bit of the error number is set, indicating an exception error, or
  (b) the flags word indicates it is a program report (ie unexpected error).
  Clicking on this button will open a command window with a *Debug prompt
  running in a simple environment - the current application cannot be replaced,
  the exit handler tidies up the command window, and errors (such as those
  caused by aborts from any comamnd line tool you use) do not cause an exit
  from the command window. As usual with *Debug, you can press the Escape key
  to resume the interrupted code, but in this case we also get the Wimp to
  redraw the error box.
Admin:
  Tested on a Risc PC. To get the most from this tool, you need Wimp 4.69, an
  as-yet uncommited version of the C library with fixed environment handling,
  and preferably BASIC 1.29.