I've been asked by my boss to write a specification for a new application module, which is alien territory for me. I'm usually given specs to work from by others, but the way they approach it goes against how I initially plan an application. I tend prototype and write notes about the application as I go along. They're more technical too, dealing with specific functional elements (validation, error handling, etc).
How do other developers tend to approach specifications? My boss needs an idea of how the application will work, so would it be considered a spec or a pitch?
I'm dealing with PHP programming language, although I'd appreciate any advice regardless of background.
Many thanks in advance