To what extent is a doppelganger supposed to look like you?

Are they supposed to look like an identical twin with only slight differences like freckles and birth marks? Or can they look very similar too you, but not quite like an identical twin. (ie: like the pairs brothers or sisters who look VERY similar, but aren't necessarily identical twins)|||Doppelganger is German for 'twin'. So there's your answer.|||they should look EXACTLY like you. maybe a different hair color or eye color, but the same expressions, the same face, the same hair style, etc. everything.|||they are by definition supposed to be identical like a twin. Doppel is german for double ganger goer