The guide is based on (approximately) MODX 2.1.3, though almost all the concepts in it are good for 2.2 and probably 2.3.
It does not cover media sources or Custom Resource Classes, which are new in 2.2 and there have been some minor changes in the Manager, though I don't think anything that would seriously throw anyone.
I'm not sure what you mean by "custom modules" (since Revolution doesn't have modules). If you mean custom snippets, plugins, and add-on components: yes. If you mean Custom Manager Pages: they are covered, but the example is a very simple CMP with no JavaScript.
I hope that helps.
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PLEASE, PLEASE specify the version of MODX you are using . . . PLEASE!
MODx info for everyone:
http://bobsguides.com/MODx.html
