A URI scheme may be defined as the topmost level in the URI naming structure in the field of computer networking. A scheme name generally defines all URIs and also the URI references which are absolute in nature. The scheme name is followed by a colon character (“:”). The remaining part of the URI is termed as the specific scheme part. There are individual specifications regulating the individual schemes. These specifications are generally used for defining the semantics and syntax associated with the remaining part or the scheme specific part.
At times, the URI schemes may be called “protocols” and this largely happens by error. They sometimes are also called URL protocols or URI protocols. This is because most URI schemes were actually designed along with a given protocol and therefore may have the same name.
cid is one of the official URI schemes registered with the IANA. One amongst several official URI schemes is IANA which is registered with IANA. The chief objective of this URI scheme or cid is to ensure that the individual parts of a given SMTP/MIME message are referenced. cid:
