The 'helpers' directory contains scripts, that aid the specification process.
The version folders ('v.') contain the specification files for a specific version. Ideally they should be created before the implementation and stay untouched. In reality they may be altered heavily during the implementation phase.
The ER diagrams are created using draw.io. The 'erd.png' files contain the graphic representation and the xml code and can therefore be loaded back into draw.io.
The constraints describe the details of the models and database tables. They use the modelspec helper to generate html code, which can be pasted into GitHub issues.