EndPosition converts an end Pos in the FileSet into a Position.

Line returns the line number for the given offset in the given file.

Offset returns f.Offset(pos), but first checks that the file contains the pos.

Offsets returns Offset(start) and Offset(end).

Pos returns f.Pos(offset), but first checks that the offset is non-negative and not larger than the size of the file.

Position returns the Position for the pos value in the given file.

StartPosition converts a start Pos in the FileSet into a Position.