2.1.12 [ISO32000-1] Section 18.104.22.168.8, Type 7 Shadings (Tensor-Product Patch Meshes)
The specification states:
Type 7 shadings (tensor-product patch meshes) are identical to type 6, except that they are based on a bicubic tensor-product patch defined by 16 control points instead of the 12 control points that define a Coons patch. The shading dictionaries representing the two patch types differ only in the value of the ShadingType entry and in the number of control points specified for each patch in the data stream.
Self-overlapping meshes are not supported.