when authoring document is html or xhtml, it is important to add a doctype declaration. the declaration must be exact (both in spelling and in case) to have the desired effect, which makes it sometimes difficult. to ease the work, below is a list of recommended declarations that you can use in your web documents.
use the following markup as a template to create a new xhtml 1.0 document using a proper doctype. see the list below if you wish to use another document type.
<?xml version=1.0 encoding=utf-8?><!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><head><title>an xhtml 1.0 strict standard template</title><meta http-equiv=content-type content=text/html;charset=utf-8 /><meta http-equiv=content-style-type content=text/css /></head><body> <p>… your html content here …</p></body></html>
<!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>
<!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>
<!doctype html public -//w3c//dtd xhtml 1.1//en http://www.w3.org/tr/xhtml11/dtd/xhtml11.dtd>
<!doctype html public -//w3c//dtd xhtml basic 1.0//en http://www.w3.org/tr/xhtml-basic/xhtml-basic10.dtd>
<!doctype html public -//w3c//dtd xhtml basic 1.1//en http://www.w3.org/tr/xhtml-basic/xhtml-basic11.dtd>
<!doctype html public -//ietf//dtd html 2.0//en>
<!doctype html public -//w3c//dtd html 3.2 final//en>
<!doctype math system http://www.w3.org/math/dtd/mathml1/mathml.dtd>
<!doctype math public -//w3c//dtd mathml 2.0//enhttp://www.w3.org/tr/mathml2/dtd/mathml2.dtd>
<!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>
<!doctype svg public -//w3c//dtd svg 1.0//enhttp://www.w3.org/tr/2001/rec-svg-20010904/dtd/svg10.dtd>
<!doctype svg public -//w3c//dtd svg 1.1//enhttp://www.w3.org/graphics/svg/1.1/dtd/svg11.dtd>
<!doctype svg public -//w3c//dtd svg 1.1 basic//enhttp://www.w3.org/graphics/svg/1.1/dtd/svg11-basic.dtd>
<!doctype svg public -//w3c//dtd svg 1.1 tiny//enhttp://www.w3.org/graphics/svg/1.1/dtd/svg11-tiny.dtd>
<!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>
<!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>
http://www.w3.org/tr/1998/rec-html40-19980424/loose.dtd
http://www.w3.org/tr/1998/rec-html40-19980424/frameset.dtd
http://www.w3.org/tr/1999/rec-html401-19991224/loose.dtd
http://www.w3.org/tr/1999/rec-html401-19991224/frameset.dtd
http://www.w3.org/tr/2000/rec-xhtml1-20000126/dtd/xhtml1-transitional.dtd
http://www.w3.org/tr/2000/rec-xhtml1-20000126/dtd/xhtml1-frameset.dtd