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Indicates whether the document is rendered in Quirks mode or Standards mode.


mode = document.compatMode 


  • "BackCompat" if the document is in quirks mode;
  • "CSS1Compat" if the document is in no-quirks (also known as "standards") mode or limited-quirks (also known as "almost standards") mode.
Is an enumerated value that can be:

Note: all these modes are now defined in standards, so the older "standards" and "almost standards" names are nonsensical and no longer used in standards.


if (document.compatMode == "BackCompat") {
  // in Quirks mode


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 Last updated by: teoli,