The internal representation of a mesh's polygon structure. This consists of an array of indices that specify the vertices in order (counter-clockwise if the normal is facing you), followed by -2 to terminate the polygon, followed by the next polygon, and so on.
When using to create a topology attribute from a polygonal description, make sure that all integers are valid vertex indices. The last polygon must be terminated. You can use any negative number to terminate a polygon when setting values, but -2 is always returned if you get this attribute.