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Valid doctype declarations

Total Validator currently recognises the following DOCTYPEs to determine the HTML specification to apply to web pages. This should normally be the first tag in the HTML page. Note that these are generally case sensitive:

(X)HTML5:
<!DOCTYPE html>
(X)HTML5 (alternative):
<!DOCTYPE html SYSTEM "about:legacy-compat">
XHTML 1.1+Aria 1.0:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+ARIA 1.0//EN" "http://www.w3.org/WAI/ARIA/schemata/xhtml-aria-1.dtd">
XHTML 1.1+RDFa 1.1:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.1//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-2.dtd">
XHTML 1.1+RDFa 1.0:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
XHTML 1.1:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
XHTML Basic 1.1:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.1//EN" "http://www.w3.org/TR/xhtml-basic/xhtml-basic11.dtd">
XHTML 1.0 Strict:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
XHTML 1.0 Loose:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
XHTML 1.0 Frameset:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
XHTML-Print 1.0:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML-Print 1.0//EN" "http://www.w3.org/TR/xhtml-print/xhtml-print10.dtd">
XHTML Basic 1.0:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN" "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
XHTML Mobile Profile 1.2:
<!DOCTYPE html PUBLIC "-//WAPFORUM//DTD XHTML Mobile 1.2//EN" "http://www.openmobilealliance.org/tech/DTD/xhtml-mobile12.dtd">
HTML 4.01+Aria 1.0:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML+ARIA 1.0//EN" "http://www.w3.org/WAI/ARIA/schemata/html4-aria-1.dtd">
HTML 4.01+RDFa 1.1:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01+RDFa 1.1//EN" "http://www.w3.org/MarkUp/DTD/html401-rdfa11-1.dtd">
HTML 4.01+RDFa Lite 1.1:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01+RDFa Lite 1.1//EN" "http://www.w3.org/MarkUp/DTD/html401-rdfalite11-1.dtd">
HTML 4.01+RDFa 1.0:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/html401-rdfa-1.dtd">
HTML 4.01 Strict:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
HTML 4.01 Loose:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
HTML 4.01 Frameset:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">
HTML 4.0 Strict:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd">
HTML 4.0 Loose:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
HTML 4.0 Frameset:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN" "http://www.w3.org/TR/REC-html40/frameset.dtd">
ISO/IEC 15445:
<!DOCTYPE html PUBLIC "ISO/IEC 15445:2000//DTD HTML//EN">
ISO/IEC 15445 (alternative):
<!DOCTYPE html PUBLIC "ISO/IEC 15445:2000//DTD HyperText Markup Language//EN">
HTML 3.2:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
HTML 3.2 (alternative):
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
HTML 3.2 (alternative):
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Draft//EN">
HTML 2.0:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
HTML 2.0 (alternative):
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">