Noun
Misspelling of referrer.
(Internet) Alternative form of referrer (“the referring URL”)
Source: en.wiktionary.orgServer administrators’ scripts typically query for particular expected values like method, or URL, or referer header, etc., but not for fake verbs. Source: Internet
The second setted property, showed in last example too, is one, that's a referer to parent constructor if exists, undefined value otherwise. Source: Internet