User Text-Entry Gadget:

  This gadget places text-entry box on your diagrams.  The text-box
  becomes active during simulations.  When text is entered in the box,
  it calls your designated function which can access the entered data.
  To place such a text-box in a diagram, instantiate a model that 
  contains the following function call:

	user_text_field( label, x, y, your_function, id );

  The label is a character string containing any initial text
  you wish to appear in the text-field.

  The x and y values are the floating-point coordinate 
  offsets where you want to place the text-box on your diagram relative 
  to the box under which it is instantiated.  An x-y value of (0.0,0.0) 
  will place the text-box at the upper left corner of the box where it is 

  The your_function is the name of the function that you want
  to be called when the text gets entered.  You should define this
  function within a DEFINE_GLOBAL: area.

  The id is an arbitrary data item that you can use to identify
  which of several text-fields the entry is coming from.

  For example:


	 /* Prototype the standard function. */
	 void user_text_field( char *label, float x, float y, 
			 void *u_func, int data_arg );

	 /* Define your (user) function. */
	 void user_texttest( Widget w, caddr_t client_data )
	   char *str1 = XmTextGetString(w);
	   printf("Form %d returned '%s'\n", client_data, str1);


	/* Define your box-model that contains a text-entry form. */

	  DEFINE_THREAD: start_up
	    user_text_field( "0.88", 0.1, 0.1, user_texttest, 101 );


  To try this example, you would create a diagram that instantiates
  a box of type Form_Box.  If you built and ran the simulation
  containing this example-model, you will see a text-box appear
  on the box.  The initial text in the box would be 0.88.

  If you type some new text and press enter, it will call the function 
  user_textform which will print:
	Form 101 returned 'whateveryoutyped'
  in your terminal window.

  You can establish any number of text-boxes, and they can call any number
  of functions that you define.