nesting <choice> and <sequence> to create arbitrary element selection in XSD

Question

I would like to validate my XML using an XSD. The XML is supposed to contain complex elements with some (none to all) elements of a given set. I think the straight foward solution for the complex element is

<xs:sequence>
  <xs:element name="foo" minOccurs="0" maxOccurs="1"/> 
  <xs:element name="bar" minOccurs="0" maxOccurs="1"/> 
  <xs:element name="bee" minOccurs="0" maxOccurs="1"/> 
</xs:sequence>

I want to get rid of the set order of elements, plus I want to get rid of the minOccurs="0" in every line, so that

<foo>text</foo>
<bee>text</bee> 
<bar>text</bar>

is also valid. My idea was to write

<xs:sequence minOccurs="0" maxOccurs="unbounded">
   <xs:choice minOccurs="0" maxOccurs="unbounded"> 
      <xs:element1>
      <xs:element2> 
      ... 
   </xs:choice>
</xs:sequence>

which should translate to "select one element of the list as many times as you want to."

But it does not allow me to put an appearance restriction (like maxOccurs=1) on individual elements. Is there a better way to validate an XML without forcing a given order of elements?