The docs for creating a custom pipeline are confusing

See

• https://groups.google.com/d/msgid/bob-devel/89dc9a68-a4bc-4849-a9b9-f3a4d79974e3n%40googlegroups.com
• https://groups.google.com/d/msgid/bob-devel/1d82d1f1-3c21-4b41-a844-3a937c086f3fn%40googlegroups.com