> This page is for version v2026-02-09 (default).
> For other versions, use one of these documentation indexes:
> - v2026-02-09 (default): https://docs.extend.ai/2026-02-09/llms.txt
> - v2025-04-21: https://docs.extend.ai/2025-04-21/llms.txt
> - v2024-12-23: https://docs.extend.ai/2024-12-23/llms.txt

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.extend.ai/llms.txt
> Use this file to discover all available pages before exploring further.
>
> ## API version
> The current API version is `2026-02-09`, served at the site root (no version prefix in URLs).
> If this page URL contains `/2025-04-21/` or `/2024-12-23/`, you are reading an older API version.
> Prefer the current docs at https://docs.extend.ai/llms.txt unless the user explicitly needs that older version.
> Do not treat older-version pages as the source of truth for new integrations.

# HTML source anchors: trace parsed blocks back to the uploaded file

> Set advancedOptions.htmlSourceAnchors in your parse config to anchor each block to its byte range in the uploaded HTML, and advancedOptions.returnSourceNodes for word-level anchors.

Set `advancedOptions.htmlSourceAnchors` to `true` in your parse config to anchor each block parsed from an HTML file to the exact byte range it came from. Anchored blocks carry a `source` object (`type`, `byteOffset`, `byteLength`) in place of `polygon`/`boundingBox`, and the run reports the encoding those offsets are measured against in `output.metadata.sourceEncoding`. Add `advancedOptions.returnSourceNodes` for word-level anchors under `output.source.nodes`, the text-format counterpart to `returnOcr.words`.

Available on API version `2026-02-09`, in Extend Studio, and with any parse engine and version. HTML files must be UTF-8 or Windows-1252 encoded; otherwise the run fails with the new `UNSUPPORTED_FILE_ENCODING` failure reason.

**SDK note:** because anchored blocks omit `polygon` and `boundingBox`, both fields are now optional in the SDK block types starting with extend-ai 2.5.0 (TypeScript), extend-ai 1.21.0 (Python), extend-java-sdk 1.22.0, and extend-go-sdk 0.9.0. Upgrading Java or TypeScript may require wrapping existing geometry access in an `Optional` or null check; Python and Go are unaffected at runtime. Responses for non-HTML parses, and for HTML parses without this option, are unchanged.

See [HTML source anchors](/parsing/response-format#html-source-anchors) and the [configuration reference](/parsing/configuration#advancedoptionshtmlsourceanchors).