A custom configuration is useful for separating the scope of dependencies needed for a dedicated purpose.

Let's say you wanted to declare a dependency on the link:https://tomcat.apache.org/tomcat-9.0-doc/jasper-howto.html[Jasper Ant task] for the purpose of pre-compiling JSP files that should _not_ end up in the classpath for compiling your source code.
It's fairly simple to achieve that goal by introducing a custom configuration and using it in a task.

							<mapper>
								<type>perm</type>
								<user>${packaging.fess.user}</user>
								<group>${packaging.fess.group}</group>
							</mapper>
						</data>
						<data>
							<type>directory</type>
							<src>${project.build.directory}/fess/WEB-INF/classes/org/codelibs/fess/tomcat</src>
							<mapper>
								<type>perm</type>

 *
 * <p>The primary way to provide the data that your hash function should act on is via a {@link
 * Hasher}. Obtain a new hasher from the hash function using {@link #newHasher}, "push" the relevant
 * data into it using methods like {@link Hasher#putBytes(byte[])}, and finally ask for the {@code
 * HashCode} when finished using {@link Hasher#hash}. (See an {@linkplain #newHasher example} of
 * this.)
 *

 *
 * <p>The primary way to provide the data that your hash function should act on is via a {@link
 * Hasher}. Obtain a new hasher from the hash function using {@link #newHasher}, "push" the relevant
 * data into it using methods like {@link Hasher#putBytes(byte[])}, and finally ask for the {@code
 * HashCode} when finished using {@link Hasher#hash}. (See an {@linkplain #newHasher example} of
 * this.)
 *

    @CanIgnoreReturnValue
    @Override
    public Hasher putInt(int i) {
      update(4, i);
      return this;
    }

    @CanIgnoreReturnValue
    @Override
    public Hasher putLong(long l) {
      update(4, (int) l);
      update(4, l >>> 32);
      return this;
    }

    @CanIgnoreReturnValue
    @Override
    public Hasher putChar(char c) {
      update(2, c);
      return this;

            hasher.putInt(bytes.length);
            hasher.putBytes(bytes);
        }

        @Override
        public void putBytes(byte[] bytes, int off, int len) {
            hasher.putInt(len);
            hasher.putBytes(bytes, off, len);
        }

        @Override
        public void putHash(HashCode hashCode) {
            hasher.putInt(hashCode.length());
            hasher.putHash(hashCode);

        when:
        hasher.hash(zipEntry('META-INF/foo'))
        hasher.hash(zipEntry('META-INF/foo/MANIFEST.MF'))
        hasher.hash(zipEntry('META-INF/properties'))
        hasher.hash(zipEntry('META-INF/build.propertiesX'))
        hasher.hash(zipEntry('bar.properties'))
        hasher.hash(zipEntry('resources/foo.properties'))
        hasher.hash(zipEntry('foo'))
        hasher.hash(zipEntry('org/gradle/foo.class'))

    }

    @Override
    public String toString() {
        return primitiveType.toString(array);
    }

    @Override
    public void appendToHasher(Hasher hasher) {
        primitiveType.appendTo(hasher, array);
    }

    @Override
    public ValueSnapshot snapshot(@Nullable Object value, ValueSnapshotter snapshotter) {
        PrimitiveType valueType = PrimitiveType.maybeOfValue(value);

// Map.Lookup require updates to the hasher, so a full Mutex lock (not a
// read-lock) is require around all Map operations if a shared
// hasher is accessed from multiple threads.
//
// If SetHasher is not called, the Map will create a private hasher at
// the first call to Insert.
func (m *Map) SetHasher(hasher Hasher) {
	m.hasher = hasher
}

// Delete removes the entry with the given key, if any.

*   [Python license example](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/ops/nn.py#L1)
*   [Java license example](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/java/src/main/java/org/tensorflow/Graph.java#L1)
*   [Go license example](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/go/operation.go#L1)