The Content-Location Header
The Content-Location header associates a URI with the part. In Figure 32, the Content-Location header contains the value http://roguewave.example/simple.txt. Other parts in the message can reference the part using the value of the Content-Location header. The URI in the header is only used by other parts within the same message. Therefore, the URI need not be world-unique or indicate an actual resource on the Internet.
RFC 2557 defines the Content-Location header in section 4.2 (p. 7).