What this check inspects
Shipwork sends the page HTML to the public W3C Nu HTML checker and reports the error and warning counts with the first few messages and their line numbers. If the page returns an error status or an empty body, it says so instead of validating nothing and reporting health.
What a failure means
Each HTML error is reported as an error. Markup errors are not a ranking factor on their own, but they cause parsing problems that break structured data, rendering and accessibility in ways that are hard to find by eye. Warnings are worth clearing but are usually cosmetic.
How to fix it
- Fix unclosed and mis-nested tags first. Those move content in the parse tree and cause the most damage.
- Correct duplicate id attributes, which break both validation and any script or label that targets the id.
- Remove element combinations the checker flags as invalid rather than assuming browsers will cope.
- Re-run the validator after a theme change, since a template edit can introduce errors site-wide.
A typical failure, worked through
The setupA theme edit leaves a div unclosed inside the product template, so the price block ends up nested inside the description element.
What the check reportsThe validator reports an error on the line, and the structured data check separately reports that price is missing, because the parser moved the element out of the Offer context.
The pointValidation errors are often the root cause behind a structured-data symptom. Fix the markup before rewriting the schema.