Documentation for CCK hooks?

I'm trying to port a couple of CCK modules from D5 to D6 (Matrix and Explainfield). I've started with Matrix. I went through it with Coder and got everything there as shipshape as I could. At this point, it installs properly, it displays the settings page properly, and it even stores the settings properly. But I haven't been able to get it to display the matrix on the node form.

I could really use a solid understanding of how the CCK-specific hooks work, but there seems to be very little info out there. There is this (http://drupal.org/node/342987) very incomplete book, but it's not sufficient.

Anyone care to share any resources and/or advice?