Meaning of upper indices of Hypergeometric1F1

Hi all,
I have a problem with the understanding of an output of Mathematica 9 and I hope that you can help me: a calculation yields the result that I have attached as an image and I do not understand the meaning of the upper indices [1,0,0]. Unfortanetly I did not find help in the documentation.

ScreenShot2015-10-29at10.14.06AM.png

Hi, it is a notation for (partial) derivatives, try this:

Derivative[1,0,0][Hypergeometric1F1]
D[Hypergeometric1F1[x,y,z],x]

Next time, you could try FullForm on your expression, it sometimes is very illuminating:

FullForm[D[f[x, y], x]]

outputs

Derivative[1,0][f][x,y]

See also tutorial/TheRepresentationOfDerivatives in the help