need ways to generate both xs:sequence and xs:attribute into a same xs:complexType, for maven

[XenoAmess]

Hi.
In maven we need such grammar like:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>acm_test</artifactId>
    <version>1.0-SNAPSHOT</version>
    <name>acm_test</name>

    <properties>
        <maven.compiler.source>23</maven.compiler.source>
        <maven.compiler.target>23</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-plugin-plugin</artifactId>
                <configuration>
                    <goalPrefix combine.self="override"/>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-release-plugin</artifactId>
                <version>2.5.1</version>
                <configuration combine.self="override">
                    <goals>deploy</goals>
                    <localCheckout>true</localCheckout>
                    <mavenExecutorId>forked-path</mavenExecutorId>
                    <tagNameFormat>${reactor.name}-@{project.version}</tagNameFormat>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>org.apache.maven.scm</groupId>
                        <artifactId>maven-scm-provider-hg</artifactId>
                        <version>1.9.2</version>
                    </dependency>
                    <dependency>
                        <groupId>org.apache.maven.scm</groupId>
                        <artifactId>maven-scm-provider-gitexe</artifactId>
                        <version>1.9.2</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>

</project>

please focuse on the <configuration combine.self="override"> part.

so we need the output xsd be:

    <xs:complexType>
      <xs:sequence>
        <xs:any minOccurs="0" maxOccurs="unbounded" processContents="skip"/>
      </xs:sequence>
      <xs:attribute name="combine.children" type="xs:string" use="optional">
  <xs:annotation>
    <xs:documentation source="version">4.0.0+</xs:documentation>
    <xs:documentation source="description">
        
        {@code combine.children}: available values are {@code merge} (default) and {@code append}.
        @see &amp;lt;a href=&amp;quot;https://maven.apache.org/pom.html#Plugins&amp;quot;&amp;gt;POM Reference documentation&amp;lt;/a&amp;gt;
        @see &amp;lt;a href=&amp;quot;https://codehaus-plexus.github.io/plexus-utils/apidocs/org/codehaus/plexus/util/xml/Xpp3DomUtils.html&amp;quot;&amp;gt;Xpp3DomUtils&amp;lt;/a&amp;gt;
        
      </xs:documentation>
  </xs:annotation>
</xs:attribute>
      <xs:attribute name="combine.self" type="xs:string" use="optional">
        <xs:annotation>
          <xs:documentation source="version">4.0.0+</xs:documentation>
          <xs:documentation source="description">
                  
                  {@code combine.self}: available values are {@code merge} (default) and {@code override}.
                  @see &amp;lt;a href=&amp;quot;https://maven.apache.org/pom.html#Plugins&amp;quot;&amp;gt;POM Reference documentation&amp;lt;/a&amp;gt;
                  @see &amp;lt;a href=&amp;quot;https://codehaus-plexus.github.io/plexus-utils/apidocs/org/codehaus/plexus/util/xml/Xpp3DomUtils.html&amp;quot;&amp;gt;Xpp3DomUtils&amp;lt;/a&amp;gt;
                  
                </xs:documentation>
        </xs:annotation>
      </xs:attribute>
    </xs:complexType>

though actually there be no ways for us to do it in modello now, as far as I get from modello sources codes.
so I want to modify some grammar of modello to add such feature.

one way be allow <fields> in <field>, and there be of course other ways, but I want to know about your ideas first.

thought1: <fields> in <field> approach?

    <class>
      <name>ConfigurationContainer</name>
      <version>4.0.0+</version>
      <description>Contains the configuration information of the container like Plugin.</description>
      <fields>
        <field>
          <name>inherited</name>
          <version>4.0.0+</version>
          <description>
            Whether any configuration should be propagated to child POMs. Note: While the type
            of this field is {@code String} for technical reasons, the semantic type is actually
            {@code Boolean}. Default value is {@code true}.
          </description>
          <type>String</type>
        </field>
        <field>
          <description>
            <![CDATA[
            <p>The configuration as DOM object.</p>
            <p>By default, every element content is trimmed, but starting with Maven 3.1.0, you can add
            {@code xml:space="preserve"} to elements you want to preserve whitespace.</p>
            <p>You can control how child POMs inherit configuration from parent POMs by adding {@code combine.children}
            or {@code combine.self} attributes to the children of the configuration element:</p>
            <ul>
            <li>{@code combine.children}: available values are {@code merge} (default) and {@code append},</li>
            <li>{@code combine.self}: available values are {@code merge} (default) and {@code override}.</li>
            </ul>

            @see <a href="https://maven.apache.org/pom.html#Plugins">POM Reference documentation</a>
            @see <a href="https://codehaus-plexus.github.io/plexus-utils/apidocs/org/codehaus/plexus/util/xml/Xpp3DomUtils.html">Xpp3DomUtils</a>
            ]]>
          </description>
          <name>configuration</name>
          <type>DOM</type>
          <fields>
            <field xml.attribute="true" xml.tagName="combine.children">
                <name>configurationCombineChildren</name>
                <version>4.0.0+</version>
                <description>
                  <![CDATA[
                  {@code combine.children}: available values are {@code merge} (default) and {@code append}.
                  @see &lt;a href=&quot;https://maven.apache.org/pom.html#Plugins&quot;&gt;POM Reference documentation&lt;/a&gt;
                  @see &lt;a href=&quot;https://codehaus-plexus.github.io/plexus-utils/apidocs/org/codehaus/plexus/util/xml/Xpp3DomUtils.html&quot;&gt;Xpp3DomUtils&lt;/a&gt;
                  ]]>
                </description>
                <type>String</type>
              </field>
              <field xml.attribute="true" xml.tagName="combine.self">
                <name>configurationCombineSelf</name>
                <version>4.0.0+</version>
                <description>
                  <![CDATA[
                  {@code combine.self}: available values are {@code merge} (default) and {@code override}.
                  @see &lt;a href=&quot;https://maven.apache.org/pom.html#Plugins&quot;&gt;POM Reference documentation&lt;/a&gt;
                  @see &lt;a href=&quot;https://codehaus-plexus.github.io/plexus-utils/apidocs/org/codehaus/plexus/util/xml/Xpp3DomUtils.html&quot;&gt;Xpp3DomUtils&lt;/a&gt;
                  ]]>
                </description>
                <type>String</type>
              </field>
          </fields>
        </field>
      </fields>
      <codeSegments>
        <codeSegment>
          <version>4.0.0+</version>
          <code>
            <![CDATA[
    public boolean isInherited() {
        return ( getInherited() != null ) ? Boolean.parseBoolean( getInherited() ) : true;
    }

            ]]>
          </code>
        </codeSegment>
        <codeSegment>
          <version>4.0.0/4.0.99</version>
          <code>
            <![CDATA[
    @Deprecated
    public void unsetInheritanceApplied() {
    }

            ]]>
          </code>
        </codeSegment>
      </codeSegments>
    </class>