Preserve target formatting when pasting Markdown

[Julia Roldi (juliaroldi)]

Summary

Update MarkdownPastePlugin to merge converted Markdown with preferTarget, preserving the destination font family, size, and color while still applying Markdown formatting such as heading boldness. Add a regression test covering Markdown pasted into preformatted content.

How to test

1. Run yarn test:fast --testPathPattern=MarkdownPastePluginTest.
2. Paste a Markdown heading into content with a custom font family, font size, and text color. Confirm the pasted heading retains those destination styles and applies the expected bold heading format.

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-08-21 16:55 UTC

[Copilot]

Pull request overview

Updates Markdown paste conversion to preserve destination formatting while retaining heading styles, with regression coverage for styled content.

Changes:

• Uses preferTarget during auto-conversion.
• Adds tests for preserving font family, size, color, and heading boldness.
• The asMarkdown path still requires target-preferred merging. Moderate, 2 votes.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Summary
packages/roosterjs-content-model-markdown/test/plugins/MarkdownPastePluginTest.ts	Adds regression coverage for styled Markdown headings.
packages/roosterjs-content-model-markdown/lib/plugins/MarkdownPastePlugin.ts	Preserves target formatting during auto-conversion; the explicit asMarkdown path still replaces custom font sizes with heading sizing.

Suppressed comments (1)

packages/roosterjs-content-model-markdown/lib/plugins/MarkdownPastePlugin.ts:98

• preferTarget overrides every segment-format key, not just font family/size/color. A target marker can carry explicit italic: false (the DOM italic handler records normal styles this way) or a non-default fontWeight, so Markdown emphasis/heading boldness is then overwritten and disappears. Use keepSourceEmphasisFormat, or merge only the destination's non-semantic font properties while retaining source emphasis.

                        mergeFormat: 'preferTarget',

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