[relaxng-user] Trang handling of (text|element) content

[J. David Eisenberg]

By "popular demand" my XML class wants to know about XML Schema.
One example is a document that consists of one or more lists.
A list consists of one or more items. Each item consists of text
or a list. (Yes, I'm teaching about recursive definitions.)
Sample document follows:

<document>
  <list>
    <item> First item outer </item>
    <item> Second item outer </item>
    <item>
      <list>
          <item> nested first </item>
      </list>
    </item>
    <item> Third item outer </item>
  </list>
</document>

Relax NG follows:

<grammar xmlns="http://relaxng.org/ns/structure/1.0">

<start>
<element name="document">
   <oneOrMore>
      <ref name="list-defn"/>
   </oneOrMore>
</element>
</start>

<define name="list-defn">
   <element name="list">
      <oneOrMore>
         <element name="item">
            <choice>
               <text />
               <ref name="list-defn"/>
            </choice>
         </element>
      </oneOrMore>
   </element>
</define>

</grammar>

Here's what Trang makes of it (with blank lines inserted for ease of
reading).

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
elementFormDefault="qualified">
  <xs:element name="document">
    <xs:complexType>
      <xs:sequence>
        <xs:element maxOccurs="unbounded" ref="list"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="list">
    <xs:complexType>
      <xs:sequence>
        <xs:element maxOccurs="unbounded" ref="item"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="item">
    <xs:complexType mixed="true">
      <xs:sequence>
        <xs:element minOccurs="0" ref="list"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

But the "item" element is NOT mixed; if you make an item mixed as 
follows, then it's invalid according to Relax NG, but not according to
XML Schema.

<item> some text and a...
   <list>
      <item>nested</item>
   </list>
</item>

My questions are:

1) Can I write an XML Schema that will do exactly the same thing that
   the Relax NG does?
2) If so, how many hoops must I jump through to accomplish it?
3) I'm sure Trang's output is reasonable, but I don't understand the
   reasoning.  Any simple explanations?

-- 
J. David Eisenberg  http://catcode.com/