Introduction to RELAX NG (1/2) - exploring XML | 2 Introduction
to RELAX NG While we have seen how elements and attributes are
defined, we also need to learn how to specify cardinality. This
is done through special elements, of which we have already seen
the |?||zero or one appearances, either appear all or nothing.|
|*||indicates any number of occurrences| |+||one to any number
of occurrences| It is also possible to specify alternatives in a
grammar, and group elements together: ||||one alternative out of
the following set| |()||a combination of elements, in the given
order| |+||allows child elements to occur in any order| RELAX NG
allows patterns to reference externally-defined datatypes, such
as those defined by the W3C XML Schema Datatypes. RELAX NG
implementations may differ in what datatypes they support. You
must use datatypes that are supported by the implementation you
plan to use. The data pattern matches a string that represents a
value of a named datatype. contains a URI identifying the
library of