The first entry refers to the point on the target object to want to anchor the start of the line too (there is no second "attachto" point al-la SetPoint()).
Code:
line1:SetStartPoint("BOTTOMLEFT", f, 10, 10)
line1:SetEndPoint("TOPRIGHT", -10, -10)
Code:
line1:SetStartPoint("BOTTOMLEFT", f, "BOTTOMLEFT", 10, 10)
Attach the start of the line to "BOTTOMLEFT" of f at offset x of "BOTTOMLEFT", and offset y of 10 with the last 10 being ignored.