From the first root cause to a clean retest
How to Fix HTML Errors
Preserve the original report, repair messages by DOM impact, and change the shared source rather than every generated page.
Step-by-step process
- Open Nu HTML Checker for the exact public URL and save the complete dated report.
- Confirm the checker received HTML rather than login/WAF/error content; preserve server source and rendered DOM separately.
- Start with the first parser/content-model error: later messages may cascade from one unclosed or wrongly nested construct.
- Find the template/component/source line; repair duplicate IDs, nesting, required attributes, and invalid element context.
- Do not remove ARIA, labels, headings, metadata, or framework attributes merely to silence the checker—verify the standard and impact.
- After a small group, rerun validation and compare DOM, visual/mobile, forms, menus, media, and JavaScript selectors.
- Repeat across representative templates and edge cases; add an automated build/CI check where possible.
Read the messages
| Type | Meaning | Action |
|---|---|---|
| Error/fatal | Conformance violation or serious parse case | Investigate first |
| Warning/info | Formally allowed but potentially problematic | Evaluate context |
| Non-document error | Checker could not fully examine the document | Repair access/input and repeat |
| Cascade | Many messages after one early error | Fix the first root cause |
Do not hand-edit generated output
When a CMS/template produces HTML, response editing disappears on the next deployment. Change the source and add a regression test.
Rollback and scope
Create a commit/backup before changes. If styles/scripts/forms break, restore the last group and compare parsed DOM before/after. Finish with the independent audit.
A validator does not replace accessibility, visual, CSS/JS, Schema.org, or functional testing.
