Yes. HTML isn't XML. As you discovered, HTML in the real world is allowed to be malformed in various ways, while XML is not. A compliant parser MUST barf on

Yes. HTML isn't XML. As you discovered, HTML in the real world is allowed to be malformed in various ways, while XML is not. A compliant parser MUST barf on various kinds of malformed text. (Search for "fatal error" in https://www.w3.org/TR/REC-xml/ https://www.w3.org/TR/REC-xml/ to verify.) This makes XML parsers inappropriate for HTML parsing. Interestingly, even perfectly valid HTML may not be valid XML. To see that consider <b>this <i>example</b> carefully</i>.