Maven assembly: copy from specific sub-folder of dependency

I'm using Maven assembly plugin to build a WAR of our product (previously done by Ant). As there're many leftovers of Apache Ant, there's one specific requirement that would make build process easier: copy specific sub-folder of dependency (e.g., jar or war resource) to a specific target sub-folder.

So far I learned that Assembly descriptors allow to specify <outputDirectory>, but is there's any chance to specify a <sourceDirectory>? E.g., I want to apply this rule for one single WAR or JAR type dependency.

Consider this example of assembly descriptor fragment (not 100% accurate):

    <dependencySet>
         <unpack>true</unpack>
         <scope>runtime</scope>
         <useProjectArtifact>false</useProjectArtifact>
         <includes>
             <include>my-specific-dependency:war</include>
         </includes>
         <outputDirectory>WEB-INF/myresources</outputDirectory>
     </dependencySet>
 

I want to say that I want to copy some folder from my-specific-dependency:war to WEB-INF/myresources.

EDIT NB: I'm aware that this is not a very correct requirement as we shouldn't know what's inside an artifact, the correct way would be declaring to extract the whole artifact to the target directory (neat declarative approach).

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