You can either submit your changes in the patches section of the sourceforge project page:
http://sourceforge.net/tracker/?grou...21&atid=388894

Or get your own private branch in Subversion. This is usually the way we work most of the time anyway. In your branch you can mess around without breaking anything, it can always be restored if needed and you don't get disturbed by other developments.
Once your changes are finished and tested they can be very easily merged into the main trunk for release.

You are welcome to contribute the way you prefer. If you need any specific help just ask here or on IRC #phex on freenode

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