understanding help description for ant Customizing

Hello,

I have some problems understanding this text in:

"Customizing the IDE-Generated Ant Script" (Standard Projects):

To add a new target to the build script:
Create the new target in build.xml.

Optionally, add the new target to the dependencies of any of the IDE's
existing targets. Override the existing target in build.xml then add the
new target to the existing target's depends property.

For example, the following adds the new-target target to the run
target's dependencies:
<target name="run" depends="new-target,init,compile"/>

Copy the dependencies exactly as they exist in build-impl.xml or
suite.xml. (-- hier comes my problem -- ) Notice that you do not need to
copy the body of the run target into build.xml. (-- --)

What does the last sentence exactly mean?

I have thought that the body of the overriden run target will not be
processed. 

I tried:
in build-impl.xml:
  <target depends="init,compile" description="Run a main class."
name="run">
        <j2seproject1:java>
            <customize>
                <arg line="${application.args}"/>
            </customize>
        </j2seproject1:java>
        <echo message=" run impl"/>
    </target>

in build.xml:
 <target depends="init,compile" description="Run a main class."
name="run"/>

will not print any output from echo.

A bug or just my misunderstanding?

Thanks! Konstantin