The <none> tag selects files that are not selected by any of the elements it contains. It returns as soon as it finds a selector that selects the file, so it is not guaranteed to check every selector.

<fileset dir="${src}" includes="**/*.php">
  <none>
    <size value="1000" when="more"/>
    <date datetime="01/01/2011 12:00 AM" when="before"/>
  </none>
</fileset>