What is CDATA in HTML

Question

What is the use of CDATA inside JavaScript tags and HTML    lt script type  text javascript  gt       lt   CDATA         gt   lt  script gt

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CDATA has no meaning at all in HTML   CDATA is an XML construct which sets a tag s contents that is normally  PCDATA - parsed character data  to be instead taken as  CDATA  that is  non-parsed character data  It is only relevant and valid in XHTML   It is used in script tags to avoid parsing  lt  and  amp   In HTML  this is not needed  because in HTML  script is already  CDATA

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All text in an XML document will be parsed by the parser  But text inside a CDATA section will be ignored by the parser  CDATA -  Unparsed  Character Data  The term CDATA is used about text data that should not be parsed by the XML parser  Characters like  quot  lt  quot  and  quot  amp  quot  are illegal in XML elements   quot  lt  quot  will generate an error because the parser interprets it as the start of a new element   quot  amp  quot  will generate an error because the parser interprets it as the start of an character entity  Some text  like JavaScript code  contains a lot of  quot  lt  quot  or  quot  amp  quot  characters  To avoid errors script code can be defined as CDATA  Everything inside a CDATA section is ignored by the parser  A CDATA section starts with  quot  lt   CDATA  quot  and ends with  quot    gt  quot   Use of CDATA in program output  CDATA sections in XHTML documents are liable to be parsed differently by web browsers if they render the document as HTML  since HTML parsers do not recognise the CDATA start and end markers  nor do they recognise HTML entity references such as  amp lt  within  lt script gt  tags  This can cause rendering problems in web browsers and can lead to cross-site scripting vulnerabilities if used to display data from untrusted sources  since the two kinds of parsers will disagree on where the CDATA section ends   A brief SGML tutorial  Also  see the Wikipedia entry on CDATA

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CDATA is a sequence of characters from the document character set and may include character entities  User agents should interpret attribute values as follows  Replace character entities with characters   Ignore line feeds   Replace each carriage return or tab with a single space

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From http   en wikipedia org wiki CDATA      Since it is useful to be able to use less-than signs   lt   and   ampersands   amp   in web page scripts  and to a lesser extent styles    without having to remember to escape them  it is common to use CDATA   markers around the text of inline  and  elements in   XHTML documents  But so that the document can also be parsed by HTML   parsers  which do not recognise the CDATA markers  the CDATA markers   are usually commented-out  as in this JavaScript example     lt script type  text javascript  gt     lt   CDATA  document write   lt          gt   lt  script gt

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A way to write a common subset of HTML and XHTML  In the hope of greater portability   In HTML   lt script gt  is magic escapes everything until  lt  script gt  appears   So you can write    lt script gt x     lt br  gt      and  lt br  gt  won t be considered a tag   This is why strings such as   x     lt  scripts gt     must be escaped like   x     lt  scri     pts gt     See  Why split the  lt script gt  tag when writing it with document write     But XML  and thus XHTML  which is a  subset  of XML  unlike HTML   doesn t have that magic   lt br  gt  would be seen as a tag    lt   CDATA  is the XHTML way to say      don t parse any tags until the next    gt   consider it all a string   The    is added to make the CDATA work well in HTML as well   In HTML  lt   CDATA  is not magic  so it would be run by JavaScript  So    is used to comment it out   The XHTML also sees the     but will observe it as an empty comment line which is not a problem        That said    compliant browsers should recognize if the document is HTML or XHTML from the initial doctype  lt  DOCTYPE html gt  vs  lt  DOCTYPE html PUBLIC  -  W3C  DTD XHTML 1 1  EN    http   www w3 org TR xhtml11 DTD xhtml11 dtd  gt  compliant websites could rely on compliant browsers  and coordinate doctype with a single valid script syntax   But that violates the golden rule of the Internet      don t trust third parties  or your product will break

User · Answer

CDATA is Obsolete   Note that CDATA sections should not be used within HTML  they only work in XML   So do not use it in HTML 5   https   developer mozilla org en-US docs Web API CDATASection Specifications

[javascript] What is CDATA in HTML?

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