I am working on a doc that will give more elaborate explanations and examples of formulas than what is in the official formula list. For the time being the doc is free, but when a market place for docs become available, I will start charging for it.
The document is far from complete, it is turning out to be quite a bit of work, but I thought it would already be useful.
There are about 30 formulas so far, there are also sections where I compare various similar formulas with each other, eg. Contains(), ContainsAll() etc.
Enjoy, feedback will be appreciated.