How exactly does dual mining work?

Question

bitcoin

How exactly does dual mining (simultaneous/parallel mining of several cryptocurrencies) work? That is, is it just the launch of two miners (which, "in theory", should not interfere with each other), or a specialized algorithm for a specific pair of cryptocurrencies?
Which clients other than Claymore allow dual mining?
Where to read about technical aspects (for a programmer, not for a miner)?
Thank you!