I've read some stuff on the wiki and there is part about "creating a subcircuit" (see attachment). It looks like it is very handy, but it can't be found on the current svn repository.
P Zoltan added in the mailing list:
"I've just checked it. There is a regression; it should be fixed. In rev
103 it worked, but now the "create sibcircuit" menu entry doesn't appear."
screenshot of the old functionality
This bug is invalid. I didn't do a "make install" on the svn version, so the "create subcircuit" did not show up. Upon installing the version it just works.