How do you specify an XSD that allows a range of elements in any order?

Question

I have some XSD that looks something like this:

<element name="a">
  <complexType>
    <sequence>
      <element name="b" type="t:typ" minOccurs="1" maxOccurs="unbounded" />
      <element name="c" type="t:typ" minOccurs="1" maxOccurs="unbounded" />
    </sequence>
  </complexType>
</element>

How would I change it so that instead of a sequence, I could allow the tags b and c to be jumbled in any order, e.g. how would I make this valid?..

<a>
  <b />
  <c />
  <b />
  <c />
  <b />
  <b />
</a>

The 'all' option sounded promising, but it seems to only allow no more than one of each of the child elements.

Answer 1

I believe you want this:

<element name="a">
  <complexType>
    <choice maxOccurs="unbounded">
      <element name="b" type="t:typ" />
      <element name="c" type="t:typ" />
    </choice>
  </complexType>
</element>

Answer 2

Could you try an unbounded sequence of choice elements? Something like this? (untested)

<element name="a"> 
  <complexType> 
    <sequence maxOccurs="unbounded" minOccurs="0">
      <choice> 
        <element name="b" type="t:typ" /> 
        <element name="c" type="t:typ" /> 
      </choice>
    </sequence>
  </complexType> 
</element>