This node marks a shader signal for output by the renderer to an AOV (Render Var). It does not actually change the signal at all.
The Type and Name must match the Source Type and Source Name of the Render Vars node.
Set your Render Var to the Raw Source Type.
On the Render Var, float or color3f are the most common values for Format.
Signature of the input signal, adapts to the input type automatically. Must match 'Source Type' on the Render Var
Name given to the output signal. Must match the 'Source Name' on the Render Var.