Simon Willison’s Weblog

Understanding Bidirectional (BIDI) Text in Unicode. It turns out you need to sanitise user input to ensure there are no unicode characters that switch your site’s regular text to RTL.

Posted 15th March 2009 at 4:37 am

Recent articles

ChatGPT agent's user-agent - 4th August 2025
The ChatGPT sharing dialog demonstrates how difficult it is to design privacy preferences - 3rd August 2025
Reverse engineering some updates to Claude - 31st July 2025

bidi 1 cal-henderson 7 filtering 2 security 532 unicode 29 userinput 1

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