%RM

This command causes all light pen sensitive fields on the screen to be made write-protected, that is, the user can select them with a light pen, but not overwrite their contents. To switch the write-protection off again, issue the command again.

For a field to be light pen sensitive, it must be displayed intensified (session parameter AD=I) or blinking (AD=B), and the first character in the field must be one of the light pen designator characters ("?", ">" ,"&" or a blank); selecting a field with a light pen causes the designator character to be changed, therefore you can make the processing of fields selected with a light pen dependent on the values of the designator characters.

See also Light Pen Support (in the Operations documentation) and the PEN value of the system variable *PF-KEY.