XML Pocket Reference, 3rd Edition

Name

rng:optional — Matches zero or one occurrences of whatever its children match

XML syntax example

<element name="date"
 datatypeLibrary="http://www.w3.org/2001/XMLSchema-
 datatypes">
 <optional>
  <element name="mydate">
   <data type="dateTime" />
  </element>
 </optional>
</element>

Compact syntax example

element date { element mydate { xsd:dateTime }? }

Parents

attribute, choice (( ) and |), define (name of pattern followed by =), element, except (-), group (( ) and ,), interleave (&), list, mixed, oneOrMore (+), optional (?), start (start followed by =), zeroOrMore (*)

Description

The optional pattern matches a pattern of zero or one of whatever its children match. In the compact syntax, optional is represented by a question mark, as in DTDs. If multiple child patterns are present, they are treated as if they were wrapped by a group pattern.

See also

§1, oneOrMore, zeroOrMore