Define element occurence options in Relax NG

To determine how often an element can occur, DTDs use symbols (e.g., *, +, ?) and XML Schemas use attributes (e.g., minOccurs, maxOccurs). Relax NG is more, well, straightforward.

In Relax NG, to state that a tag may be used zero or more times, place a wrapper tag around it called <zeroOrMore>:

   <zeroOrMore>
      <element name="mytag">
         <text/>
      </element>
   </zeroOrMore>

Similarly, for one or more occurrence, use the <oneOrMore> wrapper around the target element:

   <oneOrMore>
      <element name="mytag">
         <text/>
      </element>
   </oneOrMore>

And then for optional elements, you use the <optional> wrapper:

   <optional>
      <element name="mytag">
         <text/>
      </element>
   </optional>

Note that if there isn't an occurrence indicator on an element that it is required and can only occur once.