Historical clue formulations

• Popular online reference — 2022-02-28
• Much-visited website run by a nonprofit foundation — 2022-02-25
• Resource with content in 300+ languages — 2020-10-23
• Many teachers disallow it in footnotes — 2017-11-02
• Popular online reference — 2010-02-01
• Its symbol is a globe composed of jigsaw puzzle pieces — 2009-04-18
• Popular reference work — 2007-07-20