What does html xmlns http www w3 org 1999 xhtml do

Question

I can t believe what is happening in my website  When I add this line    lt html xmlns  http   www w3 org 1999 xhtml  gt   lt  DOCTYPE html gt   lt html gt    lt head gt    Everything works fine  And when I don t  CSS  messes  up  everything becomes different and layout becomes  ugly     How can this line solve all the problems

User · Answer

The namespace name http   www w3 org 1999 xhtml  is intended for use in various specifications such as   Recommendations       XHTML    1 0  The Extensible HyperText Markup Language     XHTML Modularization     XHTML 1 1     XHTML Basic     XHTML Print     XHTML RDFa   Check here for more detail

User · Answer

You re mixing up HTML with XHTML   Usually a  lt  DOCTYPE gt  declaration is used to distinguish between versions of HTMLish languages  in this case  HTML or XHTML    Different markup languages will behave differently  My favorite example is height 100   Look at the following in a browser   XHTML   lt  DOCTYPE html PUBLIC  -  W3C  DTD XHTML 1 0 Transitional  EN   http   www w3 org TR xhtml1 DTD xhtml1-transitional dtd  gt   lt html xmlns  http   www w3 org 1999 xhtml  xml lang  en  lang  en  gt   lt head gt     lt style type  text css  gt      table   height 100  background yellow       lt  style gt   lt  head gt   lt body gt     lt table gt       lt tbody gt         lt tr gt  lt td gt How tall is this  lt  td gt  lt  tr gt       lt  tbody gt     lt  table gt   lt  body gt   lt  html gt        and compare it to the following   note the conspicuous lack of a  lt  DOCTYPE gt  declaration   HTML  quirks mode    lt html gt   lt head gt     lt style type  text css  gt      table   height 100  background yellow       lt  style gt   lt  head gt   lt body gt     lt table gt       lt tbody gt         lt tr gt  lt td gt How tall is this  lt  td gt  lt  tr gt       lt  tbody gt     lt  table gt   lt  body gt   lt  html gt    You ll notice that the height of the table is drastically different  and the only difference between the 2 documents is the type of markup   That s nice    now  what does  lt html xmlns  http   www w3 org 1999 xhtml  gt  do   That doesn t answer your question though  Technically  the xmlns attribute is used by the root element of an XHTML document   according to Wikipedia      The root element of an XHTML document must be html  and must contain an xmlns attribute to associate it with the XHTML namespace    You see  it s important to understand that XHTML isn t HTML but XML - a very different creature   ok  a kind of different creature  The xmlns attribute is just one of those things the document needs to be valid XML  Why  Because someone working on the standard said so     you can read more about XML namespaces on Wikipedia but I m omitting that info  cause it s not actually relevant to your question    But then why is  lt html xmlns  http   www w3 org 1999 xhtml  gt  fixing the CSS   If structuring your document like so     as you suggest in your comment    lt html xmlns  http   www w3 org 1999 xhtml  gt   lt  DOCTYPE html gt   lt html gt   lt head gt              is fixing your document  it leads me to believe that you don t know that much about CSS and HTML  no offense   and that the truth is that without  lt html xmlns  http   www w3 org 1999 xhtml  gt  it s behaving normally and with  lt html xmlns  http   www w3 org 1999 xhtml  gt  it s not - and you just think it is  because you re used to writing invalid HTML and thus working in quirks mode   The above example I provided is an example of that same problem  most people think height 100  should result in the height of the  lt table gt  being the whole window  and that the DOCTYPE is actually breaking their CSS    but that s not really the case  rather  they just don t understand that they need to add a html  body   height 100     CSS rule to achieve their desired effect

User · Answer

It sounds like your site has CSS or JS that depends on running in quirks mode   Which is why you need garbage above your doctype to render  correctly    I suggest removing said garbage and then fixing your CSS JS to actually work in standards mode  you ll save yourself a lot of pain in the long run

User · Answer

Its an XML namespace  It is required when you use XHTML 1 0 or 1 1 doctypes or application xhtml xml mimetypes   You should be using HTML5 doctype  then you don t need it for text html   Better start from template like this     lt  DOCTYPE html gt   lt html gt       lt head gt           lt meta charset utf-8   gt           lt title gt domcument title lt  title gt           lt link rel  stylesheet  href   stylesheet css  type  text css    gt       lt  head gt       lt body gt               lt  -- your html content -- gt               lt script src   script js  gt  lt  script gt       lt  body gt   lt  html gt        When you have put your Doctype straight - do and validate you html and your css   That usually will sove you layout issues

[html] What does "<html xmlns="http://www.w3.org/1999/xhtml">" do?

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