Documentation for Java Vanilla Defaults

Is there anywhere I can find just... a laid out document of all the namespaces in vanilla Minecraft, or a datapack that covers all the vanilla mobs/blocks etc? I learn best by looking at what already exists and figuring out how to modify it. So for example, if I wanted to modify zombie behaviour, the first thing I want to do is be able to look at the default vanilla data for a zombie to figure out how it works - and I'm stumped on how to find this. Existing datapacks only have the things that have changed (obviously) and all the official Mojang documentation seems to be for Bedrock.