Writing merge strategy?

I need a custom merge strategy (not driver) for a tool I’m writing, and I’m wondering:

1. Is there documentation for the API anywhere?

2. Does git-merge actually do any magic, or could I just run the script that implements my merge directly?  In other words, is there really any difference between a merge strategy and a script that creates the tree I want and then commits it using git-commit-tree with multiple -p arguments.

—
Daniel M. Israel, Ph. D.
Physics Verification Lead
XCP-4: Methods & Algorithms
Mailstop F644
Los Alamos National Laboratory
505 665 5664