7.3. Specifying is not designing
The previous two chapters defined a design process for how to work with ideas and develop them into plans. The importance of a defined design process is to separate the act of designing and planning work from the act of writing a specification for it. The creation of a specification should, as much as possible, be focused on expressing an existing plan or set of decisions in the best possible way, rather than simultaneously designing that plan. The less separation there is between these two things, the harder it is to achieve either of them. Performing one of these processes on its own is difficult enough, and the more one tries to do both at the same time, the lower the odds are of doing either task properly.
Spec authors must be aware of the different mindsets of designing and specifying. When they sit down to write the specification, they must, for the moment, stop exploring and creating and focus on expressing and explaining. Or, at least they must plan to come back and heavily revise the document to reflect the voice of an explainer rather than a creator. Whenever writing specifications (or anything else), it's important to remember that the way that we figured something out is not always the best way to explain it to someone else.
7.3.1. Describing the final design versus how to build it
While it's possible to combine feature and technical specifications into one document, most of the time they need to be clearly separated sections. One ...