In the context of web documents, the term HTML validator technically refers to validation using DTDs by SGML tools. However, the common (non technical) use of the term refers to checking an HTML document for various problems using some type of computerized checker, and not necessarily by using a DTD with SGML tools. Furthermore, the term HTML validation for HTML5 cannot mean validation using a DTD because HTML5 is not SGML-based and does not use a DTD.
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