HF-131 (7/7): documentation

[marcin-kordas-hoc]

What and why

Stacked on #1766, the last in this stack. Documentation only.

• Adds the missing #SPILL! row to docs/guide/types-of-errors.md (the type existed and was
  producible before this stack, just undocumented) and a new "Error messages and explanations"
  section explaining what message does and doesn't do: it states the specific cause within an
  error's type, but HyperFormula does not turn it into a longer plain-language explanation or call
  out to an LLM to generate one — an application wanting to rephrase for end users should do so at
  the application layer, using type/message as input.
• Adds a paragraph to docs/guide/custom-functions.md explaining hasMessage (HF-131 (3/7): a consumer can tell 'no message' from 'empty message' #1763) for authors
  of custom functions.

No src/ changes in this PR.

Verified

• npm run docs:build — clean, both new docs pieces present in rendered output
• Full private test suite reproduced against this branch's tip — no regressions beyond the same
  pre-existing branch-pinning mismatch as the rest of this stack (unaffected by a docs-only change,
  included for completeness since it's the tip of the stack)

Stack

7 of 7 — stacked on #1766. Last PR in the HF-131 stack: #1761 → #1762 → #1763 → #1764 → #1765 →
#1766 → this one.

🤖 Generated with Claude Code

---

Note

Low Risk
Documentation-only; no runtime or API behavior changes.

Overview
Documentation-only update to docs/guide/types-of-errors.md.

Adds #SPILL! to the guide tags and error table (no space for an array result to spill when non-empty cells would be overwritten). Introduces Error messages and explanations, clarifying that each error’s message pinpoints the cause within its type, that HyperFormula does not expand messages into longer prose or use an LLM for that, and that apps should rephrase or translate errors for end users using type and message.

^{Reviewed by Cursor Bugbot for commit 5d90bec. Bugbot is set up for automated code reviews on this repo. Configure here.}

[qunabu]

Task linked: HF-131 Verbose and actionable formula error messages

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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[cursor]

Tag list exceeds the ten-tag limit

Low Severity

Adding #SPILL! brings the tags list to 11 entries. VuePress search indexes only title, tags, and headings, and the project cap is 10 tags per page so extra tags can crowd out more relevant hits once the 10-result limit applies.

 

^{Triggered by learned rule: VuePress tags frontmatter invariants}

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	hyperformula-docs	5d90bec	Commit Preview URL Branch Preview URL	Sep 11 2026, 05:38 AM

[github-actions]

Performance comparison of head (5d90bec) vs base (d56bd3d)

                                     testName |    base |    head | change
--------------------------------------------------------------------------
                                      Sheet A |  505.95 |  513.34 | +1.46%
                                      Sheet B |  162.82 |  167.22 | +2.70%
                                      Sheet T |  144.72 |  148.24 | +2.43%
                                Column ranges |  483.06 |  484.23 | +0.24%
                                Sorted lookup | 15211.5 | 14722.9 | -3.21%
Sheet A:  change value, add/remove row/column |   16.46 |   16.58 | +0.73%
 Sheet B: change value, add/remove row/column |   148.1 |  148.75 | +0.44%
                   Column ranges - add column |  159.09 |  157.59 | -0.94%
                Column ranges - without batch |  491.55 |  491.17 | -0.08%
                        Column ranges - batch |  122.84 |  121.87 | -0.79%

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.40%. Comparing base (d56bd3d) to head (5d90bec).

Additional details and impacted files

@@                       Coverage Diff                       @@
##           fix/hf-131-issue-444-addresses    #1767   +/-   ##
===============================================================
  Coverage                           97.40%   97.40%           
===============================================================
  Files                                 195      195           
  Lines                               15834    15834           
  Branches                             3491     3491           
===============================================================
  Hits                                15423    15423           
  Misses                                403      403           
  Partials                                8        8           

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