RFC 2616 - the lost characters
4. If the message uses the media type “multipart/byteranges”, and the ransfer-length is not otherwise specified, then this self-elimiting media type defines the transfer-length. This media type UST NOT be used unless the sender knows that the recipient can arse it; the presence in a request of a Range header with ultiple byte- range specifiers from a 1.1 client implies that the lient can parse multipart/byteranges responses.
I really have no clue where those characters went, but “the sender knows that the recipient can arse it” sounds kinda rude ;). It’s strange that either nobody ever saw these typos or they didn’t bother. Do RFCs get updated for fixing typos? I found some more.