From the W3C 2004 recommendation:
"4.6 Predefined Entities
[Definition: Entity and character references MAY both be used to escape the left angle bracket, ampersand, and other delimiters. A set of general entities (amp, lt, gt, apos, quot) is specified for this purpose. Numeric character references MAY also be used; they are expanded immediately when recognized and MUST be treated as character data, so the numeric character references “<” and “&” MAY be used to escape < and & when they occur in character data.]"
I’ve run into more than one situation where this is being used.