A few things:
1. svndumpfilter can take multiple args, e.g.
$ svndumpfilter include /x /y /z > mydump
to include /x, and /y, and /z. It can’t, however, do both include and exclude at once. In theory, you can run multiple dumps when you later load them, so you could (sort of; see below) accomplish the sameish thing with
$ svndumpfilter include /x > mydumpx
$ svndumpfilter include /y > mydumpy
$ svndumpfilter include /z > mydumpz
2. HOWEVER, if you have ever MOVED a file within the repository between (in the example above), /x and /y, you can’t rely upon doing it piecewise. That’s because the references within the loading process during the load of /y will no longer be valid as they point to /x/whatever.
3. It is commonly suggested that one edit “Node-path:” entries within the dump in order to fix up directory structure issues. NOTE that you MUST also change “Node-copyfrom-path:” in the same manner. Trickily, Node-copyfrom-path is only present in nodes that were (surprise!) copied from another node. This is of course tied to 2. above.
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What is all this about, you ask? Well, it turns out that if you have a single respository with a lot of sprawling projects all under /trunk, you might need to break them out. (For example, if you intend to upload your repository dump to someone like a CVSDude or Beanstalk).
The error message that got me was something like:
svnadmin: File not found: revision 91, path ‘/trunk/x/whatever’