Welp I started modding EQ2 when the doc file was all we had. There's actually a fair bit of useful info in that file, but several essential things are missing. Since then a good deal of the essentials have been added to the FAQ of this site.
Early authors did a great job sharing discoveries in the Dev forumns of this site. Most everything you might need to know has been posted somewhere in there. Off the top of my head, there are threads that cover conditionals, concatination, data sources, menus, lists, image editing, packlock and packprop, pathing across window branches, all slash commands, addressing inventory slots, namespaces, working with UIBuilder, etc.
I posted a list of helpful links at one point. You could prbly find it with search
