<bdi> Addresses the correct display of dynamic content in a hybrid text orientation environment, ensuring punctuation and neutral characters are rendered correctly by automatically detecting and isolating text in unknown directions. 1. When embedding text with unknown directions in documents with known directions (such as Arabic usernames in English pages), the browser's Unicode bidirectional algorithm may misalign text; 2. The <bdi> element enables the browser to automatically judge the internal text direction and isolate it from surrounding content; 3. Applicable to user-generated content, dynamic data and multilingual interfaces; 4. Unlike the and dir attributes that require predicting the direction, <bdi> has intelligent detection capabilities; 5. Modern browsers support <bdi>, which does not support it but can be handled through a downgrade scheme. Therefore, when displaying multilingual content that is not written by yourself, you should use the <bdi> tag to avoid layout confusion.
The HTML <bdi></bdi>
element is specifically designed to handle birdreflectional text — content that may be displayed in either left-to-right (like English) or right-to-left (like Arabic or Hebrew) scripts — without requiring manual intervention to ensure correct text rendering.

This is especially useful when you're displaying user-generated or dynamic content whose language and direction you can't predict in advance.
What problem does <bdi></bdi>
solve?
In birdrectional text, browsers use the Unicode Bidirectional Algorithm (UBA) to determine how text should be displayed. However, when embedding text of an unknown direction within a document of a known direction (eg, inserting Arabic names into an English page), the algorithm can get confused — especially with punctuation, numbers, or mixed-language strings — leading to incorrectly ordered text.

For example, imagine an English (LTR) page displaying a list of usernames, some of which are in Arabic (RTL). Without proper isolation, the browser might incorrectly position parentses or numbers next to the username.
<!-- Without bdi — might render incorrectly --> <p>User: ???? (Online)</p>
The parentses or other neutral characters might end up in the wrong place.

How <bdi>
helps
The <bdi>
element tells the browser: "Treat this piece of text as directedly isolated from its surroundings." It automatically detects the correct direction based on the content.
<p>User: <bdi>????</bdi> (Online)</p>
Now the browser will:
- Determine the direction of the text inside
<bdi>
(in this case, RTL due to Arabic). - Isolate that text from surrounding LTR context.
- Render the parentses and other neutral characters correctly.
When to use <bdi>
Use <bdi>
in these common scenarios:
- User-generated content : Displaying usernames, comments, or posts where language and direction are unknown.
- Dynamic data : Rendering names, titles, or labels from a database or API that may contain mixed scripts.
- Multilingual interfaces : Applications supporting both RTL and LTR languages.
Examples:
<ul> <li>User: <bdi>JohnDoe123</bdi> (Online)</li> <li>User: <bdi>????_2023</bdi> (Online)</li> <li>User: <bdi>Zhang Wei</bdi> (Online)</li> </ul>
Each of these will be directly isolated, so punctuation and layout stay correct regardless of script.
Key differences from <bdo></bdo>
and dir
-
<bdo></bdo>
(bidirectional override) forces a specific direction, ignoring natural text direction. Use it only when you need to override the default behavior. - The
dir
attribute sets direction explicitly (dir="rtl"
ordir="ltr"
), but requires you to know the direction in advance. -
<bdi></bdi>
is "smart" — it auto-detects direction and isolates the text, making it ideal for unpredictable content.
Browser support and fallback
<bdi></bdi>
is supported in all modern browsers, including recent versions of Chrome, Firefox, Safari, and Edge. Internet Explorer does not support it, so if you need to support older environments, consider:
- Polyfilling (though limited),
- Using
dir
attributes with language detection, - Or gracefully accepting minor rendering issues in rare cases.
Summary
- Use
<bdi></bdi>
for text with unknown or variable direction. - It automatically isolates and detects text direction.
- Ideal for usernames, dynamic content, and multilingual apps.
- Prefer over
<bdo></bdo>
or manualdir
when direction isn't known upfront.
Basically, if you're displaying text you didn't write yourself and it might be in any language, wrap it in <bdi></bdi>
. It's a small tag that prevents big layout surprises.
The above is the detailed content of How to handle bidirectional text with the HTML bdi element. For more information, please follow other related articles on the PHP Chinese website!

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