support for <xs:alternative> from XML Schema 1.1

[vandenoever]

This validator gives an error on an XML Schema 1.1 that contains <xs:alternative/>.

java -jar xjparse-app-3.0.0.jar -S alternative.xsd test.xml

This is the error:
The content of 'message' must match (annotation?, (simpleType | complexType)?, (unique | key | keyref)*)). A problem was found starting at: alternative.

Here is example.xsd (copied from the XSD 1.1 spec):

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning" elementFormDefault="qualified" vc:minVersion="1.1">
  <xs:complexType name="messageType" mixed="true">
    <xs:sequence>
      <xs:any processContents="skip" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute name="kind">
      <xs:simpleType>
        <xs:union>
          <xs:simpleType>
            <xs:restriction base="xs:string">
              <xs:enumeration value="string"/>
              <xs:enumeration value="base64"/>
              <xs:enumeration value="binary"/>
              <xs:enumeration value="xml"/>
              <xs:enumeration value="XML"/>
            </xs:restriction>
          </xs:simpleType>
          <xs:simpleType>
            <xs:restriction base="xs:string"/>
          </xs:simpleType>
        </xs:union>
      </xs:simpleType>
    </xs:attribute>
    <xs:anyAttribute processContents="skip"/>
  </xs:complexType>
  <xs:complexType name="messageTypeString">
    <xs:simpleContent>
      <xs:restriction base="messageType">
        <xs:simpleType>
          <xs:restriction base="xs:string"/>
        </xs:simpleType>
      </xs:restriction>
    </xs:simpleContent>
  </xs:complexType>
  <xs:complexType name="messageTypeBase64">
    <xs:simpleContent>
      <xs:restriction base="messageType">
        <xs:simpleType>
          <xs:restriction base="xs:base64Binary"/>
        </xs:simpleType>
      </xs:restriction>
    </xs:simpleContent>
  </xs:complexType>
  <xs:complexType name="messageTypeXML">
    <xs:complexContent>
      <xs:restriction base="messageType">
        <xs:sequence>
          <xs:any processContents="strict"/>
        </xs:sequence>
      </xs:restriction>
    </xs:complexContent>
  </xs:complexType>
  <xs:element name="message" type="messageType">
    <xs:alternative test="@kind='string'" type="messageTypeString"/>
    <xs:alternative test="@kind='base64'" type="messageTypeBase64"/>
    <xs:alternative test="@kind='binary'" type="messageTypeBase64"/>
    <xs:alternative test="@kind='xml'" type="messageTypeXML"/>
    <xs:alternative test="@kind='XML'" type="messageTypeXML"/>
    <xs:alternative type="messageType"/>
  </xs:element>
</xs:schema>

[vandenoever]

After setting the default for xsd11 in com.nwalsh.parsers.XJParser to true, the error message changes:
java.lang.IllegalArgumentException: No SchemaFactory that implements the schema language specified by: http://www.w3.org/XML/XMLSchema/v1.1 could be loaded

[vandenoever]

This was tested with two different openjdk version:

openjdk version "1.8.0_212"
OpenJDK Runtime Environment (build 1.8.0_212-ga)
OpenJDK 64-Bit Server VM (build 25.212-bga, mixed mode)

and

OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.3+7)
Eclipse OpenJ9 VM AdoptOpenJDK (build openj9-0.14.0, JRE 11 Linux amd64-64-Bit Compressed References 20190417_202 (JIT enabled, AOT enabled)
OpenJ9   - bad1d4d06
OMR      - 4a4278e6
JCL      - 5cc996a803 based on jdk-11.0.3+7)