schema puzzle

hi.
The XMLSchema 1.0 say the "choice","sequence"in a "group" can't be 
restricted by "minOccurs"and "maxOccurs".But you can find this code like 
below in the schema 
<http://www.w3.org/2001/SMIL20/smil20-language.xsd>http://www.w3.org/2001/SMIL20/smil20-language.xsd 
is this schema is irregular??

<http://www.w3.org/2001/SMIL20/smil20-language.xsd#>- <group 
name="simpleAnimationGroup">
<http://www.w3.org/2001/SMIL20/smil20-language.xsd#>-     <choice 
minOccurs="0" maxOccurs="unbounded">
           <element ref="smil20lang:animate" />
           <element ref="smil20lang:set" />
      </choice>
</group>

thands!