(T^T)What is the SUTransformation meanning In C++ API Of Sketchup?

what is it meanning in this 4x4matrix of the image above ?
this is the C++ SDK of SU,not the Ruby.

   | R T |

M = | 0 w | ===> | a11 a12 a13 a14|
| a21 a22 a23 a24|
| a31 a32 a33 a34|
| a41 a42 a43 a44|

I had known the ( a41 a42 a43 ) means the origin Of Coordinate of the group, but I don’t know what
the R means : | a11 a12 a13|
| a21 a22 a23|
| a31 a32 a33|
I guess it was the rotation exchange matrix of coordinate ,but it seems annother meanning.
who konws the right answer? (T^T)…

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