Specifying QUIET="1" hides the contents of this element. This is useful for providing computer specifiations in places where it's implied or the spec cannot combine well with the text. For instance, when writing that a machine is monochrome, one could write 'This computer is monochrome, i.e. it has <COLOURS>2</COLOURS> colours'.
This would probably look a bit weird, in which case it can be changed to 'This computer is monochrome. <COLOURS QUIET="1">2</COLOURS>'. This would look better, and the required property (colours: 2) would be entered into the database.