This word, or the adjective
"OPTIONAL", mean that an item is truly optional. One vendor may choose to include the item
because a particular marketplace requires it or because the vendor feels that
it enhances the product while another vendor may omit the same item. An
implementation which does not include a particular option MUST be prepared to interoperate
with another implementation which does include the option, though perhaps with
reduced functionality. In the same vein an implementation which does include a
particular option MUST be prepared to interoperate with another implementation
which does not include the option (except, of course, for the feature the
option provides.)
within normative text, may
indicates a course of action permissible within the limits of the document
(ISO/IEC). [CC:2006]