A friend of mine, a Swedish national, is moving to London, and has decided to apply for an optional residence permit, info about which is found here https://www.gov.uk/eea-registration-certificate
My question is: what form does it actually take? Is it a visa-type sticker in the passport, an A4 paper sheet, or something else?
If it's a sticker, how is it issued if you apply for it on the basis of an ID Card, rather than a passport?