1) HTML 2.0 표준 문서 형식
< !DOCTYPE html PUBLIC "=//IETF//DTD HTML 2.0//EN">

2) HTML 3.2 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">

3) HTML 4.01 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
< !DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
< !DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">

4) HTML 5 표준 문서 형식 : HTML 버전 5는 DTD가 없다.
< !DOCTYPE html>

5) XHTML 1.0 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">

6) XHTML 1.1 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

7) XHTML 2.0 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 2.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml2.dtd">

8) XHTML Basic 1.0 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN" "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">

9) XHTML Basic 1.1 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.1//EN" "http://www.w3.org/TR/xhtml-basic/xhtml-basic11.dtd">

10) MahML 1.01 표준 문서 형식
< !DOCTYPE math SYSTEM "http://www.w3.org/Math/DTD/mathml1/mathml.dtd">

11) MathML 2.0 표준 문서 형식
< !DOCTYPE math PUBLIC "-//W3C//DTD MathML 2.0//EN" "http://www.w3.org/TR/MathML2/dtd/mathml2.dtd">

12) XHTML + MathML + SVG 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0 plus SVG 1.1//EN" "http://www.w3.org/2002/04/xhtml-math-svg/xhtml-math-svg.dtd">

13) SVG 1.0 표준 문서 형식
< !DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN" "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">

14) SVG 1.1 Full 표준 문서 형식
< !DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">

15) SVG 1.1 Basic 표준 문서 형식
< !DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Basic//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-basic.dtd">

16) SVG 1.1 Tiny 표준 문서 형식
< !DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Tiny//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-tiny.dtd">

17) XHTML + MathML + SVG Profile (XHTML as the host language) 표준 문서 형식
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0 plus SVG 1.1//EN" "http://www.w3.org/2002/04/xhtml-math-svg/xhtml-math-svg.dtd">

18) XHTML + MathML + SVG Profile (Using SVG as the host) 표준 문서 형식
< !DOCTYPE svg:svg PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0 plus SVG 1.1//EN" "http://www.w3.org/2002/04/xhtml-math-svg/xhtml-math-svg.dtd">

웹표준 문서 구조
< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">


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DOCTYPE 코드 구분
일반형식(Transitional) : HTML 4.01 Transitional 예전에 있었거나 없어진 태그도 지원함
엄격한형식(Strict) : HTML을 업격하게 적용 해야 한다.