Module 16: Validation, Debugging, and Practical Projects
Validate HTML and Understand Conformance
Use a validator to catch structural errors and understand what validation can and cannot prove.
A page can appear correct in a browser and still contain invalid markup. Browsers are designed to recover from many authoring errors, so visual rendering alone is not proof that the document is conforming.
Use the Nu Html Checker or another reputable HTML conformance checker to find issues such as duplicate IDs, invalid nesting, missing required attributes, and elements used in the wrong context. Read the explanation rather than blindly changing code to silence a warning.
Validation is one check, not the finish line. A document can pass an HTML validator and still be inaccessible, confusing, insecure, slow, or factually wrong. A useful review combines HTML validation, keyboard testing, a basic screen-reader check, browser developer tools, responsive testing, and manual review of links, labels, alternative text, and heading structure.
Run validation after meaningful changes, not only at the end of a project. Errors are easier to fix when the section is still fresh in your mind.