TaskDeclaration

First of all you need to declare the task in your build file: 

    <taskdef name="xcluder" 
        classname="gr.abiss.xcluder.XercesXcluder" 
        classpathref="some.classpath.id" 
    />

Alternatively ommiting the classpathref attribute (or equal) should work just fine if you place the XCluder JAR in $ANT_HOME/lib (%ANT_HOME%\lib on windows).

Use

Using the task after declaring it is rather straighforward. A typical example is: 

    <xcluder in="${source.file.path}" 
        out="${result.file.path}" 
        encoding="${encoding}" 
        indent="yes" 
    />