defining a leading bullet for unordered lists

Hello xmlschema-developers,

I am trying to right a schema for an unordered list where the first 
character must be a dot, wave dash or simple a dash. But something is 
not working :-(

This is my idea:

<xs:element name="lists">
<xs:complexType>
<xs:choice>
<xs:element name="listUnordered">
<xs:complexType mixed="true">
<xs:choice maxOccurs="unbounded" minOccurs="0">
<xs:element name="list_dot" type="dotType"/>
<xs:element name="list_dash" type="dashType"/>
<xs:element name="list_wavedash" type="wavedashType"/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name="listOrdered">
<xs:complexType mixed="true">
<xs:choice maxOccurs="unbounded" minOccurs="0">
<xs:element name="list_level1"/>
<xs:element name="list_level2"/>
<xs:element name="list_level3"/>
</xs:choice>
</xs:complexType>
</xs:element>
</xs:choice>
</xs:complexType>
</xs:element>

<xs:simpleType name="wavedashType">
<xs:restriction base="xs:string">
<xs:pattern value="~"/>
</xs:restriction>
</xs:simpleType>

<xs:simpleType name="dashType">
<xs:restriction base="xs:string">
<xs:pattern value="–"/>
</xs:restriction>
</xs:simpleType>

<xs:simpleType name="dotType">
<xs:restriction base="xs:string">
<xs:pattern value="•"/>
</xs:restriction>
</xs:simpleType>


The problem is that the pattern for the simpleType does not work. I also 
tried to use unicode characters but still the same.

Thank you for helping me,
Andreas