Source code documentation
The Gekko source code is freely available (under the open-source GNU GPL licence), and it is the intention to keep the source code well-documented.
Please note that there are some differences regarding the actual source code for Gekko 2.0, and the above documentation. This is because Gekko 2.0 has been developed quite a lot since the source code documentation was written, but the documentation is still a really good starting point regarding Gekko 2.0!
Above, there is also a link to the upcoming API (Application programming interface). For now, only the TimeSeries class is documented (but still, this is an important class regarding a timeseries-oriented software like Gekko).
Due to the large number of changes in syntax and underlying parsing methodology, the source code regarding Gekko 2.0 has long been in a state of flux. As soon as the code stabilizes a bit more, for instance in a version 2.2, it is the intention to revise the source code documentation, and augment the API to include more classes and methods.