http://www.rfc-editor.org/rfc/rfc7459.txt
RFC 7459: Representation of Uncertainty and Confidence in the Presence Information Data Format Location Object (PIDF-LO), M. Thomson, J. Winterbottom2015-02-01T23:00:00-00:00This document normatively updates the definition of location information representations defined in RFCs 4119 and 5491. It also deprecates related terminology defined in RFC 3693.