Command: save_text_image
  
Syntax: 
  s3 = save_text_image(s1, s2)
  
Description: 
  Save a rectangular region of text from a text-mode screen.
  The result is a sequence of sequences containing ASCII characters
  and attributes from the screen. You can redisplay this text using 
  display_text_image(). s1 is a 2-element sequence {line1, column1}
  specifying the top-left character. s2 is a sequence 
  {line2, column2} specifying the bottom right character.
  
Comments: 
  Because the character attributes are also saved, you will get 
  the correct foreground and background color for each character
  if you redisplay the text.
  
  An attribute byte is made up of two 4-bit fields that 
  encode the foreground and background color of a character.
  The high-order 4 bits determine the background color, while
  the low-order 4 bits determine the foreground color.
  
  This routine only works in text modes.
  
  You might use this function in a text-mode graphical user 
  interface to save a portion of the screen before displaying a 
  drop-down menu, dialog box, alert box etc.
  
  If you are flipping video pages, note that this function reads
  from the current active page.
  
Example: 
     If the top 2 lines of the screen have: 
  Hello 
  World
       
       s = save_text_image({1,1}, {2,5})
       
       Then s is something like: 
       {"H-e-l-l-o-",
                 "W-o-r-l-d-"}
       where we have indicated the attribute bytes by '-'
           
See Also: 
  display_text_image, save_image, set_active_page
  
