if there are four coplanar nodes, changing the order is enough to ensure that the resulting quad is not concave.

if the original element was not be concave to begin with, the result might be false. you can easily draw examples of non-concave hexes where four coplanar nodes form a quad partially outside the hex. but that should be checked before using this class. if we have concave elements in the mesh it gets way more complicated and a lot of the methods here might provide false results.