[3] 
>
:"MAY":
This word or the adjective "OPTIONAL" means that this item
is truly optional.  One vendor may choose to include the
item because a particular marketplace requires it or
because it enhances the product, for example; another
vendor may omit the same item.

;; [CITE@en[RFC 1123 - Requirements for Internet Hosts - Application and Support]] ([TIME[2010-07-22 04:07:59 +09:00]] 版) <http://tools.ietf.org/html/rfc1123#page-11>

* メモ

[1]
[CITE@en[XML Query (XQuery) Requirements]] ([CODE[2007-03-17 06:39:09 +09:00]] 版) <http://www.w3.org/TR/2007/NOTE-xquery-requirements-20070323/#terminology-may>
([[名無しさん]])


[2]
[CITE@en[XML Query (XQuery) 1.1 Requirements]] ([TIME[2007-03-16 09:42:40 +09:00]] 版) <http://www.w3.org/TR/2007/WD-xquery-11-requirements-20070323/#terminology-may>
([[名無しさん]])