Sources are remote files you can link to your project.

When you "pull" down a source a versioned copy is created in the project "Files".

Source Order Source Type Source Address Source Path Date Updated Source Actions
Google Docs gdoc://1QpXTQHAcvKF63Y902LQuU7nMI5DtdLf… 3 years, 1 month ago
Uploaded file upload://Open Office Slides Test.odp Open Office Slides Test.odp 3 years, 1 month ago