Which corner do UVs start in on default three.js planeGeometry?

I'm writing a deformer which modifies the position of a plane's vertices, using UVs as a completion ratio – so if the UV of a vertex is (.5,.5), it's in the center of the plane. An image linked from (Three.js) Custom Mesh UV Display Texture Properly shows UVs starting in the top left: But my deformer seems to be flipped vertically unless I treat the UVs as starting in the bottom left corner instead. OpenGL ES has different UV coordinates? says OpenGL UVs start in the bottom-left corner, and http://answers.unity3d.com/questions/154324/how-do-uvs-work.html suggests it's this way in Unity too. Which does three.js use? Extra Credit: I understand from Correct UV mapping Three.js that the answer is in planeGeometry.js somewhere – can anyone show where?