Pre-processing extension points
You can use these extension points to run an Ant target before or after the pre-processing stage. If necessary, you can also run an Ant target before a specific pre-processing step — but this approach is not recommended.
Tip: 
      For maximum compatibility with future versions of
            DITA-OT, most plug-ins should use the extension points that run before or after
            pre-processing.
- depend.preprocess.pre
- Runs an Ant target before the pre-processing stage.
- depend.preprocess.post
- Runs an Ant target after the pre-processing stage.
Legacy pre-processing extensions
The following extension points are available in the original preprocess pipeline that was used
        by default for all transformations prior to DITA-OT 3.0. These extensions are not available in the newer
        map-first pre-processing pipeline (preprocess2), which
        is used in the PDF and HTML Help transformations as of DITA-OT 3.0.
CAUTION: 
      The internal order of pre-processing steps is
            subject to change between versions of DITA-OT. New versions may remove, reorder, combine, or add steps to
            the process, so the extension points within the pre-processing stage should only be used if
            absolutely necessary.
- depend.preprocess.chunk.pre
- Runs an
            Ant target before the chunkstep in the pre-processing stage.
- depend.preprocess.coderef.pre
- Runs an
            Ant target before the coderefstep in the pre-processing stage.
- depend.preprocess.conref.pre
- Runs an
            Ant target before the conrefstep in the pre-processing stage.
- depend.preprocess.conrefpush.pre
- Runs
            an Ant target before the conrefpushstep in the pre-processing stage.
- depend.preprocess.clean-temp.pre
- Runs
            an Ant target before the clean-tempstep in the pre-processing stage.
- depend.preprocess.copy-files.pre
- Runs
            an Ant target before the copy-filesstep in the pre-processing stage.
- depend.preprocess.copy-flag.pre
- Runs
            an Ant target before the copy-flagstep in the pre-processing stage.
- depend.preprocess.copy-html.pre
- Runs
            an Ant target before the copy-htmlstep in the pre-processing stage.
- depend.preprocess.copy-image.pre
- Runs
            an Ant target before the copy-imagestep in the pre-processing stage.
- depend.preprocess.copy-subsidiary.pre
- Runs an Ant target before the copy-subsidiarystep in the pre-processing stage.
- depend.preprocess.debug-filter.pre
- Runs an Ant target before the debug-filterstep in the pre-processing stage.
- depend.preprocess.gen-list.pre
- Runs
            an Ant target before the gen-liststep in the pre-processing stage.
- depend.preprocess.keyref.pre
- Runs an
            Ant target before the keyrefstep in the pre-processing stage.
- depend.preprocess.maplink.pre
- Runs an
            Ant target before the maplinkstep in the pre-processing stage.
- depend.preprocess.mappull.pre
- Runs an
            Ant target before the mappullstep in the pre-processing stage.
- depend.preprocess.mapref.pre
- Runs an
            Ant target before the maprefstep in the pre-processing stage.
- depend.preprocess.move-meta-entries.pre
- Runs an Ant target before the move-meta-entriesstep in the pre-processing stage.
- depend.preprocess.topicpull.pre
- Runs
            an Ant target before the topicpullstep in the pre-processing stage.