referer

Etymology

The misspelling of referrer was introduced in the original proposal by computer scientist Phillip Hallam-Baker to incorporate the "Referer" header field into the HTTP specification. The misspelling was set in stone by the time (May 1996) of its incorporation into the Request for Comments standards document RFC 1945 (which "reflects common usage of the protocol referred to as 'HTTP/1.0'" at that time); document co-author Roy Fielding remarked in March 1995 that "neither one (referer or referrer) is understood by" the standard Unix spell checker of the period. "Referer" has since become a widely used spelling in the industry when discussing HTTP referrers; usage of the misspelling is not universal, though, as the correct spelling "referrer" is used in some web specifications such as the Referrer-Policy HTTP header or the Document Object Model.