I don't know much lisp and Emacs completion framework details, but if you use company-mode there's a nice article explaining how to create a new company backend
http://sixty-north.com/blog/writing-the-simplest-emacs-company-mode-backend
There's also a second part improving the backend with extra information.
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Darlan
mThanks as always,Hi,I am thinking of turning my marking stuff into a minor mode (http://matt.hackinghistory.ca/2015/07/15/mailing-subtrees-with-attachments/). One feature that is missing from my current setup is a function that will let me use org-contacts-complete-name to complete names when I'm in certain headlines (level 2). Does anyone know how to do that? I don't understand the completion framework in emacs, looks so complicated...