This quick & easy demo shows how to open an HTML document and validate it in CSE HTML Validator (you can also easily validate URLs but this is not shown in this demo). Note that the demo is based on an old version of CSE HTML Validator and requires Adobe Flash Player but the demo is still relevant to the latest version.
The validation results appear in the Results Window. You can click a validator message to go to the relevant source line in the document. Fix the problem and repeat the validation. Style (CSS) errors are shown in the Styles tab.
The demo also shows how to enable and use accessibility checking, check links, disable messages you don't want to see, change a message's type (like from error to warning), find misspelled words, and more.