dir="auto" dramatically simplifies dealing with variable and user-generated content whose language is not known.
It'd also allow site generators that convert from formats like Markdown to almost automagically support mixed-direction document with almost no changes to the generator — they just has to slap dir=auto all over the place. While not perfect, it's about the best that can be done when the input doesn't contain language information.
Browser support: Firefox, Chromium, Safari, Opera
To be useful for flipped layout, you'd also need to support CSS logical properties e.g. `text-align: start`:
Ideally dir="auto" should also trigger bidi isolation
but that's pretty orthogonal — most of the value here is in autodetected base direction and automatically flipped layout.
See a specific request for isolation support in Edge at
Here are some test results that may help:
dir isolation https://www.w3.org/International/tests/repo/results/the-dir-attribute-isolation
(click on the links in the left-most column to run the tests)
Support for isolation is really a fundamental requirement for languages using Arabic and Hebrew and other scripts such as Thaana, Syriac, N'Ko, etc. Note also that the Arabic script is the second most widely used script around the world after the Latin script, so this affects a lot of people. And the lack of isolation is not an edge-case problem (see worked examples at http://w3c.github.io/i18n-drafts/articles/inline-bidi-markup/index.en#staticexamples). It's hard to understand why Edge still doesn't support isolation for any use of the dir attribute and for bdi per the HTML standard. Unfortunately, the best recommendation for users of RTL scripts around the world is currently to use another browser than Edge.
Edge and IE are the only one not supporting this: https://www.w3.org/International/tests/repo/results/the-dir-attribute-auto