This skeleton FDW simply throws away any data it receives. Updates and deletes are no-ops, since there is no data to update or delete. Selecting data from it returns an empty resultset, of course.
This code as partly written as a bit of fun for pgCon 2013, and partly so there would be a skeleton FDW that could be used as the basis for creating another FDW. Simply take this code, globally replace the word "blackhole" (preserving case) with your FDW's prefix and you will have a new functional FDW you can start adding data handling features to.
The code includes the new new data modifying stuff as well as the pre-9.3 data scanning functionality.
The comments in the functions come from the draft 9.3 docs as at the time of writing (May 26 2013). That saves you from having to go back and forth between the docs and the code.