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Asked: 2026-05-17T21:05:16+00:00

I have a doctype declaration as seen in the first 2 lines. In the

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I have a doctype declaration as seen in the first 2 lines.

In the third line, the html tag also has some xmlns declaration and xml:lang and lang. Is any of these xmlns, xml:lang, or lang repetitive? Do they duplicate anything from the doctype. I’d like to keep the doctype and remove all the declarations on the third line if they’re repetitive.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

</html>
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1 Answer

  1. Editorial Team

    They’re not repetitive. The XML namespace for XHTML and the doctype declaration aren’t the same. Neither are the xml:lang and lang attributes. The XHTML 1.0 specification requires that all of these are included.

    The attribute list for the <html> element as described by the XHTML 1.0 Strict DTD is as follows:

    <!ATTLIST html
  %i18n;
  id          ID             #IMPLIED
  xmlns       %URI;          #FIXED 'http://www.w3.org/1999/xhtml'
  >

    (where %i18n is an internal entity that represents the xml:lang, lang and dir internationalization attributes, see below)

    Notice the fourth line. It says that xmlns is an attribute of a given URI value, and is fixed at that very namespace URL. That means if you omit the attribute or give it a different namespace, your document is invalid strict XHTML.

    The %i18n entity corresponds to these attributes:

    <!-- internationalization attributes
  lang        language code (backwards compatible)
  xml:lang    language code (as per XML 1.0 spec)
  dir         direction for weak/neutral text
-->
<!ENTITY % i18n
 "lang        %LanguageCode; #IMPLIED
  xml:lang    %LanguageCode; #IMPLIED
  dir         (ltr|rtl)      #IMPLIED"
  >

    The lang attribute is for backwards compatibility (i.e. HTML ≤ 4.01), and xml:lang is described by XML 1.0 (hence the xml namespace seen here). I’m not too sure of the exact reason why xml:lang should precede lang, but it makes sense given that XHTML is merely HTML “reworded” into XML syntax (so to speak).

    The dir attribute defaults to ltr (left-to-right text) if not specified, hence it’s not a required attribute.

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