Alt-N - Line Numbers
 Toggle the display of line numbers within the source code window.
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 This option will toggle the displaying of line numbers in the source code
 window.

 With this option to set on (default), line numbers will appear at the start
 of each line in the source code window. As you scroll the source code window
 left and right, the line numbers will stay in the same position.

 You may turn this option off, if you prefer more space for your source code.