Different Definition of LinearInterpolate

Hi,
I’m new in UE4 and when I watched the material tutorials last night I found the definition of ‘LinearInterpolate’ is different in UE4 and official web like images below.But after I test I think official web is right. Please tell me if I misunderstand the meaning of LinearInterpolate. By the way the version I used is UE4.10 in Chinese.



confusion.jpg

Thanks a lot!