The behaviours of all elements are part of the architecture

Explanation

The behavior of each element is part of the architecture insofar as that behavior can be used to reason about the system. This does not mean that the exact behavior and performance of every element must be documented in all circumstances. 

Some aspects of behavior are fine-grained and below the architect’s level of concern. But to the extent that an element’s behavior influences another element or influences the acceptability of the system as a whole, this behavior must be considered, and should be documented, as part of the software architecture.