The AttribCreate SOP can be used to provide various object-specific attributes by allowing both a label and a value to be given to the newly created attribute.
In this example, the AttribCreate SOP is used to control the width of a curve at rendertime. There are two versions, chosen by a Switch SOP.
One AttribCreate SOP gives a constant width attribute in the X axis.
The other uses an expression to control the thickness of the curve to create a tapering effect.
The attribute is used by Mantra at render time. To see the results, right-click on the render icon in the viewport, and choose "render_example".