QBS documentation does not cover "input" entity in Artifact

Considering the code like this:

Artifact

{ filePath: '.obj/' + qbs.getHash(input.baseDir) + '/' + input.fileName + '.cc' fileTags: "cc" }

it is not at all obvious or documented which class is "input" exactly and where to look at for a list of its properties. There are a few usage examples such as in Rule item docs, but otherwise documentation for this is either missing or buried deep enough that it's hard to find.