idNostringUnique id for inter-element referencing
extensionNoExtension[]Additional content defined by implementations
contentTypeNocodeMime type of the content, with charset etc.
languageNocodeHuman language of the content (BCP-47)
dataNobase64BinaryData inline, base64ed
urlNourlUri where the data can be found
sizeNounsignedIntNumber of bytes of content (if url provided)
hashNobase64BinaryHash of the data (sha-1, base64ed)
titleNostringLabel to display in place of the data
creationNodateTimeDate attachment was first created