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

V&A East Storehouse and Operation Mincemeat in London - 27th August 2025
The Summer of Johann: prompt injections as far as the eye can see - 15th August 2025
Open weight LLMs exhibit inconsistent performance across providers - 15th August 2025

bidi 1 cal-henderson 7 filtering 2 security 541 unicode 29 userinput 1

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