substitution group

XML Schema Part 0: Primer:

XML Schema provides a mechanism, called substitution groups, that allows elements to be substituted for other elements. More specifically, elements can be assigned to a special group of elements that are said to be substitutable for a particular named element called the head element. (Note that the head element as well as the substitutable elementsmust be declared as global elements.)

The following demonstrates substitution group:

<complexType name="GH6Usage">
  <sequence>
    <element ref="ipo:gh6head"/>
    <element name="gh6head2" type="string" />
    <element name="city"   type="string"/>
  </sequence>
</complexType>

<element name="gh6head" type="string" abstract="true"/>
<element name="gh6sub1" type="string" substitutionGroup="ipo:gh6head" />
<element name="gh6sub2" type="string" substitutionGroup="ipo:gh6head" />
<element name="gh6head2" type="string" abstract="true"/>
<element name="gh6sub3" type="string" substitutionGroup="ipo:gh6head2" />
<element name="gh6sub4" type="string" substitutionGroup="ipo:gh6head2" />

There are two substitution groups ipo:gh6head and ipo:gh6head2, but only ipo:gh6head is used in GH6Usage. The second element gh6head2 is named the same as ipo:gh6head2, but it is a local element of GH6Usage. Here’s what scalaxb generates:

case class GH6Usage(gh6head: rt.DataRecord[Any],
  gh6head2: String,
  city: String)

object GH6Usage extends rt.ElemNameParser[GH6Usage] {
  val targetNamespace: Option[String] = Some("http://www.example.com/IPO")
  
  def parser(node: scala.xml.Node): Parser[GH6Usage] =
    (((rt.ElemName(targetNamespace, "gh6sub2")) ^^ 
      (x => rt.DataRecord(x.namespace, Some(x.name), x.node.text))) | 
    ((rt.ElemName(targetNamespace, "gh6sub1")) ^^ 
      (x => rt.DataRecord(x.namespace, Some(x.name), x.node.text)))) ~ 
      (rt.ElemName(targetNamespace, "gh6head2")) ~ 
      (rt.ElemName(targetNamespace, "city")) ^^
        { case p1 ~ 
      p2 ~ 
      p3 => GH6Usage(p1,
      p2.text,
      p3.text) }
        
  def toXML(__obj: GH6Usage, __namespace: Option[String], __elementLabel: Option[String]): scala.xml.NodeSeq = {
    var __scope: scala.xml.NamespaceBinding = scala.xml.TopScope
    __scope = scala.xml.NamespaceBinding("xsi", "http://www.w3.org/2001/XMLSchema-instance", __scope)
    __scope = scala.xml.NamespaceBinding("ipo", "http://www.example.com/IPO", __scope)
    __scope = scala.xml.NamespaceBinding(null, "http://www.example.com/IPO", __scope)
    val node = toXML(__obj, __namespace, __elementLabel, __scope)
    node match {
      case elem: scala.xml.Elem =>
        elem % new scala.xml.PrefixedAttribute(__scope.getPrefix(rt.Helper.XSI_URL),
          "type",
          "ipo:GH6Usage", elem.attributes)
      case _ => node
    }
  }
  
  def toXML(__obj: GH6Usage, __namespace: Option[String], __elementLabel: Option[String], __scope: scala.xml.NamespaceBinding): scala.xml.NodeSeq = {
    var attribute: scala.xml.MetaData  = scala.xml.Null
    
    scala.xml.Elem(rt.Helper.getPrefix(__namespace, __scope).orNull,
      __elementLabel getOrElse { error("missing element label.") },
      attribute, __scope,
      Seq.concat(rt.DataRecord.toXML(__obj.gh6head, targetNamespace, __obj.gh6head.key, __scope),
        scala.xml.Elem(rt.Helper.getPrefix(None, __scope).orNull, "gh6head2", scala.xml.Null, __scope, scala.xml.Text(__obj.gh6head2.toString)),
        scala.xml.Elem(rt.Helper.getPrefix(None, __scope).orNull, "city", scala.xml.Null, __scope, scala.xml.Text(__obj.city.toString))): _*)
  }
  

}