Basically what the title says. To be Porphyrogennetoi (Purple-born) a royal had to be born in the Porphýra/Porphyry Chamber in the Great palace, to the reigning Basileus and and his wife, who had been created an Augusta. However, I've never seen it mentioned one way or the other if the children of a Symbasileus, or Co-Emperor, counted as being Porphyrogennetoi. Legally their father would be a reigning (albeit junior) Basileus and their mother an Empess, so would/did they count or not?