Narinder Claire asked a seemingly innocent question on the Spirit mailing list the other day. After starting to write an answer I realized that this question is not innocent at all as it touches the very fabric of Spirit: the rules of attribute handling. Many people have a hard time to properly understand what is going on in the nether regions of Spirit. More importantly, they have a hard time to understand why is Spirit implemented the way it is.
The new article Attribute Propagation and Attribute Compatibility not only answers Narinders questions but tries to explain those important concepts in more detail.