2.1.11 [ISO32000-1] Section 8.7.4.5.7, Type 6 Shadings (Coons Patch Meshes)

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V0011:

The specification states:

 Patches can sometimes appear to fold over on themselves—for example, if a boundary curve intersects itself. As the value of parameter u or v increases in parameter space, the location of the corresponding pixels in device space may change direction so that new pixels are mapped onto previous pixels already mapped.

Microsoft Edge:

Self-overlapping meshes are not supported.