MIME header content representation, allowing to get the content associated and the next value associated on the same header (if were defined).
This structure represents a single MIME header instance found on a message. To get the MIME header name (left part of a MIME heeader definition) use vortex_frame_mime_header_name.
To get the content associated to this MIME header instance use vortex_frame_mime_header_content.
To check if there are more instances defined for the same MIME header name, use vortex_frame_mime_header_next.