Which statement about validating markup is true?

• A. Validation always passes when code is well-formed.
• B. Validation results are always reliable.
• C. If a validator finds an error, the remaining code on the page may fail validation, even if the remaining code is actually valid.
• D. Validation errors only occur in HTML attributes.

Answer: (C)

Validating markup means checking the document against the rules of the HTML specification, including how tags are nested and how attributes are formed. The validator reads the file and tracks the current parsing state as it goes. If it encounters an error early—such as a missing closing tag or a malformed attribute—that problem can throw off the parser’s interpretation of the rest of the document. Because subsequent content is analyzed in that compromised context, the validator may report errors for code that would be valid if the initial issue were fixed. So it’s quite possible for later parts of the page to fail validation even though those parts are valid when considered in isolation.

Keep in mind that simply being well-formed does not guarantee validity; validation checks conformance to the standard, not just syntactic correctness. Errors can occur anywhere in markup, not only in attributes. And validator results aren’t perfectly flawless—different tools may handle edge cases in slightly different ways, so it’s important to review the reported issues and test across validators.