Use cases in the framework:

• Service integrations in the framework such as

  flutter/packages/flutter/lib/src/widgets/spell_check.dart

  Lines 312 to 414 in ad268e2

  	List<TextSpan> _buildSubtreesWithComposingRegion(
  	List<SuggestionSpan>? spellCheckSuggestions,
  	TextEditingValue value,
  	TextStyle? style,
  	TextStyle misspelledStyle,
  	bool composingWithinCurrentTextRange) {
  	final List<TextSpan> textSpanTreeChildren = <TextSpan>[];
  	int textPointer = 0;
  	int currentSpanPointer = 0;
  	int endIndex;
  	SuggestionSpan currentSpan;
  	final String text = value.text;
  	final TextRange composingRegion = value.composing;
  	final TextStyle composingTextStyle =
  	style?.merge(const TextStyle(decoration: TextDecoration.underline)) ??
  	const TextStyle(decoration: TextDecoration.underline);
  	final TextStyle misspelledJointStyle =
  	style?.merge(misspelledStyle) ?? misspelledStyle;
  	bool textPointerWithinComposingRegion = false;
  	bool currentSpanIsComposingRegion = false;
  	// Add text interwoven with any misspelled words to the tree.
  	if (spellCheckSuggestions != null) {
  	while (textPointer < text.length &&
  	currentSpanPointer < spellCheckSuggestions.length) {
  	currentSpan = spellCheckSuggestions[currentSpanPointer];
  	if (currentSpan.range.start > textPointer) {
  	endIndex = currentSpan.range.start < text.length
  	? currentSpan.range.start
  	: text.length;
  	textPointerWithinComposingRegion =
  	composingRegion.start >= textPointer &&
  	composingRegion.end <= endIndex &&
  	!composingWithinCurrentTextRange;
  	if (textPointerWithinComposingRegion) {
  	_addComposingRegionTextSpans(textSpanTreeChildren, text, textPointer,
  	composingRegion, style, composingTextStyle);
  	textSpanTreeChildren.add(
  	TextSpan(
  	style: style,
  	text: text.substring(composingRegion.end, endIndex),
  	)
  	);
  	} else {
  	textSpanTreeChildren.add(
  	TextSpan(
  	style: style,
  	text: text.substring(textPointer, endIndex),
  	)
  	);
  	}
  	textPointer = endIndex;
  	} else {
  	endIndex =
  	currentSpan.range.end < text.length ? currentSpan.range.end : text.length;
  	currentSpanIsComposingRegion = textPointer >= composingRegion.start &&
  	endIndex <= composingRegion.end &&
  	!composingWithinCurrentTextRange;
  	textSpanTreeChildren.add(
  	TextSpan(
  	style: currentSpanIsComposingRegion
  	? composingTextStyle
  	: misspelledJointStyle,
  	text: text.substring(currentSpan.range.start, endIndex),
  	)
  	);
  	textPointer = endIndex;
  	currentSpanPointer++;
  	}
  	}
  	}
  	// Add any remaining text to the tree if applicable.
  	if (textPointer < text.length) {
  	if (textPointer < composingRegion.start &&
  	!composingWithinCurrentTextRange) {
  	_addComposingRegionTextSpans(textSpanTreeChildren, text, textPointer,
  	composingRegion, style, composingTextStyle);
  	if (composingRegion.end != text.length) {
  	textSpanTreeChildren.add(
  	TextSpan(
  	style: style,
  	text: text.substring(composingRegion.end, text.length),
  	)
  	);
  	}
  	} else {
  	textSpanTreeChildren.add(
  	TextSpan(
  	style: style, text: text.substring(textPointer, text.length),
  	)
  	);
  	}
  	}
  	return textSpanTreeChildren;
  	}

  , and Support iOS 18 formatting menu #150068. Since TextEditingController.buildTextSpan returns a TextSpan, it's difficult to update the returned span to add new styles without a update method.
• maybe: Linkify

Use cases outside the framework

• Updating an existing InlineSpan with new styles, especially when you only have the InlineSpan representation.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

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