Might need to be profiled

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:composable:very" 
    xmlns:xs="http://www.w3.org/2001/XMLSchema" 
    xmlns="urn:composable:very" 
    version="1.0" 
    finalDefault="extension"

<xs:element name="Letter" type="LetterType"/>
<xs:complexType name="LetterType">
    <xs:attribute name="value" type="xs:string" use="required"/>
    <xs:attribute name="uppercase" type="xs:boolean" use="optional"/>
</xs:complexType>

<xs:element name="Punctuation" type="PunctuationType"/>
<xs:complexType name="PunctuationType">
    <xs:attribute name="value" type="xs:string" use="required"/>
</xs:complexType>

<xs:element name="Spec" type="SpecType"/>

<xs:complexType name="SpecType">
    <xs:choice minOccurs="10" maxOccurs="unbounded">
        <xs:element ref="Letter"/>
        <xs:element ref="Punctuation"/>
    </xs:choice>
</xs:complexType>

</xs:schema>