The Math Working Group has published MathML Media-type Declarations as a Group Note. Internet Media Types are used in email, HTTP and other places to indicate the format of documents. This Note contains media types for MathML. They were previously published as part of the MathML3 specification. The Note serves to give them a separate, stable address, as the MathML version 3 specification is replaced by version 4 and possibly other versions after that.
Original source: https://www.w3.org/blog/news/archives/9629