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I know about:Tabs goes to the New Tab page, and about:blank goes to a predictably blank page.

But how and why did this function come about? And are there other keywords that come after about: with different functions?

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The about: is a URI scheme. As explained here on the Wikipedia page on the about URI scheme:

about is an internal URI scheme (also known as a "URL scheme" or, erroneously, "protocol") implemented in various Web browsers to reveal internal state and built-in functions. It is an IANA officially registered scheme, and is standardized.

So this is basically an internal web browser URI that is reserved for doing specific things within a web browser. What things? As the official IANA (Internet Assigned Numbers Authority) web site, on a basic level it’s stuff like this:

  • about:blank: The about:blank URI references a blank page.
  • about:invalid: The about:invalid URI references a non-existent document with a generic error condition. It can be used when a URI is necessary, but the default value shouldn't be resolveable as any type of document.
  • about:srcdoc: Used as the document's address of iframe srcdoc documents in HTML.
  • about:legacy-compat: For use in DOCTYPEs in HTML documents when needed for compatibility with XML tools.
  • about:html-kind: The about:html-kind URI identifies the vocabulary of kind values in HTML specifications from W3C and WhatWG.

That said, what I listed above are just the bare basics: Look at the Wikipedia article again to find browser specific about: URI schemes.

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    about:robots in Firefox is a good one. May 17, 2019 at 7:12

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