Check the markup (HTML, XHTML, …) of Web documents
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<html lang="it">
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Many Document Types based on XML need a mandatory xmlns="" on the root element. For example, the root element for XHTML will look like: <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
xmlns=""
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">