Add automatic text direction detection + Right to Left Capbilities

[Karlee Wong (KarleeWong)]

Summary

Adds opt-in automatic text direction detection based on the first strong directional character in the active block.

Changes

• Update setModelDirection to:
  • Combine paragraph text segments.
  • Ignore leading numbers, whitespace, and punctuation.
  • Determine direction from the first letter, LTR mark, or RTL mark.
  • Default to LTR when no strong directional character exists.
• Export setModelDirection for model-level use.
• Add AutoDirectionPlugin.
  • Handles regular insertText input.
  • Handles compositionEnd for IME keyboards.
  • Updates direction without invoking the public API or focusing the editor.
• Export the plugin from roosterjs-content-model-plugins.
• Register the plugin in the RoosterJS demo.
• Add model and plugin unit tests.

Behavior

• שלום English uses RTL.
• Hello שלום uses LTR.
• 123 مرحبا uses RTL because leading numbers and punctuation are ignored.
• Content without a strong directional character defaults to LTR.
• Existing editors are unchanged unless AutoDirectionPlugin is registered.

Video

Recording.2026-08-25.115834.mp4

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[Julia Roldi (juliaroldi)]

Could this be part of AutoFormatPlugin? we just need to create an option called auto direction to enable and disabled this feature.

[Julia Roldi (juliaroldi)]

We already have the setDirection function, can we modify setDirection to get the changes you did in setModelDirection. What do you think?

[Jiuqing Song (JiuqingSong)]

Need to be careful when we call formatContentModel. Try only call it when we are sure we want to modify the model. So better check the input before we call this API. Because >99.9% cases we don't need to change the direction.

[Jiuqing Song (JiuqingSong)]

It seems the EndOfLine character is different so it is hard to tell what is changed.

[Julia Roldi (juliaroldi)]

I think we can use the setDirection api from roosterjs-content-model-api package.

[Karlee Wong (KarleeWong)]

Updated in 6bc76b6. AutoFormatPlugin now calls setDirection(editor, 'auto') after the cheap DOM direction check confirms a change is needed.

[Julia Roldi (juliaroldi)]

We already have the selection on line 299, why not reuse it here?

[Karlee Wong (KarleeWong)]

Updated in 6bc76b6. The regular insertText path now passes the existing selection.range into handleAutoDirection, so it only calls getDOMSelection once.

[Julia Roldi (juliaroldi)]

Can we handle auto direct and other keyboard events together?

[Karlee Wong (KarleeWong)]

Updated in 6bc76b6. Auto direction is now handled in the same input-data switch as the existing keyboard features; compositionEnd remains a separate event path for IME input.

[Jiuqing Song (JiuqingSong)]

Please fix tests