It's the "ht" in http & html
... or is somehow visible with 
more than one address (for example, via its filename and also via its library name
... [DOC] [TLE] RFC 2616 - Hypertext Transfer Protocol -- HTTP/1.1 - IETF Tools [PAR] This specification defines the protocol referred to as "HTTP/1.1", and is an ...... A 
proxy is a forwarding agent, receiving requests for a URI in its absolute ... Certain 
basic rules are in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc.