<plugin>
    <artifactId>maven-assembly-plugin</artifactId>
    <configuration>
        <descriptors>
            <descriptor>${project.basedir}/src/main/assembly/a.xml</descriptor>
            <descriptor>${project.basedir}/src/main/assembly/b.xml</descriptor>
        </descriptors>
    </configuration>
    <executions>
        <execution>
            <id>A-assembly</id>
            <phase>package</phase>
            <goals><goal>single</goal></goals>
            <configuration>
                <archive><manifest><mainClass>com.marginallyclever.a.A</mainClass></manifest></archive>
                <descriptorRefs><descriptorRef>jar-with-dependencies</descriptorRef></descriptorRefs>
            </configuration>
        </execution>
        <execution>
            <id>B-assembly</id>
            <phase>package</phase>
            <goals><goal>single</goal></goals>
            <configuration>
                <archive><manifest><mainClass>com.marginallyclever.b.B</mainClass></manifest></archive>
                <descriptorRefs><descriptorRef>jar-with-dependencies</descriptorRef></descriptorRefs>
            </configuration>
        </execution>
    </executions>
</plugin>

Maven builds project-version.jar, project-version-A.jar, project-version-B.jar and project-version-jar-with-dependencies.jar. All have manifest main class A.

Please tell me what am I doing wrong.