sets the read only flag. When this flag is true, no editing can be performed on the document (any such attempt produces an error message). Saving read only documents is inhibited as well; you must affirmatively answer a prompt to save a document with the read only flag set. This flag is automatically set whenever you open a file that you cannot write to. See Open.
If you invoke
ReadOnly with no arguments, it will toggle the flag. If you
specify 0 or 1, the flag will be set to false or true, respectively. A lower
case ‘r’ will appear on the status bar if the flag is true.