The WHY often will be elaborate enough that it deserves a design document that includes things like: who is the owner of those requisites, what is the rationale behind them, who are the stakehilders who signed off, what interactions it has other components, what alternative designs were considered, etc.
The WHY often will be elaborate enough that it deserves a design document that includes things like: who is the owner of those requisites, what is the rationale behind them, who are the stakehilders who signed off, what interactions it has other components, what alternative designs were considered, etc.