  Developers use and contribute to repositories on GitHub. Documentation
present in the repositories serves as an important source by helping developers
to understand, maintain and contribute to the project. Currently, documentation
in a repository is diversified, among various files, with most of it present in
ReadMe files. However, other software artifacts in the repository, such as
issue reports and pull requests could also contribute to documentation, without
documentation being explicitly specified. Hence, in this paper, we propose a
taxonomy of documentation sources by analyzing different software artifacts,
developer interviews and card-sorting approach. We inspected multiple artifacts
of 950 public GitHub repositories, written in four different programming
languages, C++, C#, Python and Java, and analyzed the type and amount of
documentation that could be extracted from these artifacts. To this end, we
observe that, about 25.93% of information extracted from all sources proposed
in the taxonomy contains error-related documentation, and that pull requests
contribute to around 18.21% of extracted information.
