feat: Add data-nesting-level to HTML export

[YousefED]

Summary

Adds a data-nesting-level attribute to the flattened HTML export of blocks, preserving nesting metadata.

Rationale

Previously, nested blocks were flattened in the HTML export to keep the output structure simple. However, this meant that indentation information was lost for non-list blocks.
With this change, blocks are still flattened in the export (maintaining simplicity), but we now include a data-nesting-level attribute. This metadata allows consumers to apply appropriate styling (e.g., margins) or process the nesting structure without needing a complex nested DOM structure.

Changes

• Modified serializeBlocksExternalHTML.ts to track nestingLevel during recursive serialization.
• Added data-nesting-level attribute to the output HTML element if nestingLevel > 0.
• Updated snapshots to reflect the new attribute.

Impact

• HTML Export: The exported HTML will now include data-nesting-level attributes on nested blocks. This is a non-breaking change but affects the output HTML string.

Testing

• Automated Tests:
  • Existing snapshots for HTML export have been updated to include the new attribute.
  • Verified via pnpm test (snapshots updated by user).

Checklist

• Code follows the project's coding standards.
• Unit tests covering the new feature have been added. (Snapshot tests updated)
• All existing tests pass.
• The documentation has been updated to reflect the new feature (N/A - internal serialization change)

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Review	Updated (UTC)
blocknote	Ready	Preview	Jan 2, 2026 6:28pm
blocknote-website	Ready	Preview	Jan 2, 2026 6:28pm

[pkg-pr-new]

Open in StackBlitz

@blocknote/ariakit

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/ariakit@2329

@blocknote/code-block

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/code-block@2329

@blocknote/core

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/core@2329

@blocknote/mantine

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/mantine@2329

@blocknote/react

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/react@2329

@blocknote/server-util

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/server-util@2329

@blocknote/shadcn

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/shadcn@2329

@blocknote/xl-ai

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/xl-ai@2329

@blocknote/xl-docx-exporter

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/xl-docx-exporter@2329

@blocknote/xl-email-exporter

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/xl-email-exporter@2329

@blocknote/xl-multi-column

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/xl-multi-column@2329

@blocknote/xl-odt-exporter

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/xl-odt-exporter@2329

@blocknote/xl-pdf-exporter

npm i https://pkg.pr.new/TypeCellOS/BlockNote/@blocknote/xl-pdf-exporter@2329

commit: 5f9fd91

[nperez0111]

I'm increasingly worried about this "simplicity" in the html export. It is more work to maintain and I'm unsure what the benefits are.

Ultimately, HTML is a machine readable format. If someone wanted to parse the full export into a "simple" export, then it really should be up to them, not part of the core package. (I hold a similar position for markdown, that it should be outside of the core & not shipped to users who will not use it)

[YousefED]

I'm increasingly worried about this "simplicity" in the html export. It is more work to maintain and I'm unsure what the benefits are.

Ultimately, HTML is a machine readable format. If someone wanted to parse the full export into a "simple" export, then it really should be up to them, not part of the core package. (I hold a similar position for markdown, that it should be outside of the core & not shipped to users who will not use it)

Agree, the solution we should work towards is to extract all renderers (whether it's exporters or to the editor) to be independent from the core editor / block definitions