What is xml cdata?

Source: Internet
Author: User
Tags xml cdata xml parser
    • CDATA considerations:
Parse data

The XML Parser usually processes all text in the XML document.

When an XML element is parsed, the text inside the XML element is also parsed:


< Message > This text is also parsed </ Message >



The XML parser does this because the XML element may also contain other elements. In the following example, the name element contains the first and last elements:


< Name > < First > Bill </ First > < Last > Gates </ Last > </ Name >



The parser will consider the aboveCodeYes:

< Name >
< First > Bill </ First >
< Last > Gates </ Last >
</ Name >


Escape characters

Invalid xml characters must be replaced with corresponding entities.

If you use a character similar to "<" in the XML document, the parser will encounter an error because the parser considers this as the beginning of a new element. Therefore, the Code should not be written as follows:


< Message > If salary < 1000 Then </message >



To avoid this situation, you must convert the character "<" to an object, as shown below:

< Message > If salary & Lt; 1000 then </ Message >



Below are the five pre-defined in the XML documentEntity:

& Lt; < Yu no.
& Gt; > Yu no.
& Amp; & And
& Apos; ' Single quotes
& Quot; " Double quotation marks

The object must start with the symbol "&" and end with the symbol.

Note: Only the "<" and "&" characters are strictly forbidden for XML. The rest are legal. It is a good habit to use entities to reduce errors.

CDATA parts

All content in CDATA is ignored by the parser.

If the text contains many "<" characters and "&" characters, it is likeProgramThe Code is the same, so it is best to put them all in the CDATA component.

A CDATA part starts with "<! [CDATA ["Mark start, end with"]> "mark:

< Script >
<! [CDATA [
Function Matchwo (A, B)
If ( < B && A <   0 ) Then
Return   1
Return   0
] >


In the previous example, all texts between CDATA components are ignored by the parser.

CDATA considerations:

1.CDATA components cannot be nested ). If the CDATA part contains the character "]>" or "<! [CDATA [", which may cause errors.

2.Note that there is no space or line break between the string "]>.

<! [CDATA []> what does it mean ???
========================================================== ==========

If the mark is plain text, <> & characters cannot be directly stored in XML, which must be escaped. However, this mark does not need to be escaped and these symbols are stored in XML documents.
This prevents unexpected special characters from causing XML parsing errors.

C # questions about xml cdata and validation effectiveness
I was just learning about XML. Here I met a CDATA segment. The explanation here is that everything in CDATA will be ignored by the parser. I don't know what this means. In simple terms, it is the use of CDATA and what is the use of the content here. If this is used, what will happen.
There is also the validation of XML validity. What does this mean? Why is it necessary to verify the validity? How is it generally verified? How is it done? I read a book and said there are two methods of DTD and XML Schema. What is the difference between them?
Although there are more problems, there are two main problems. I hope you will know how to help your younger brother. Let me know in plain words. Thank you very much.
========================================================== ============

When you use flash and XML for website applications, for example, when people enter their names freely, people can enter some symbols, for example: "<", "> ","/","? When the XML is generated, the XML structure is broken and data is interrupted.

This requires the use of XML CDATA

All text in the XML document will be parsed by the parser.

Only the text in the CDATA part is ignored by the parser.

<! [CDATA []> what does it mean ?~

Read data from the database to generate an XML file, and add "<! [CDATA []> "what does it mean?
Response. Write "<body> <! [CDATA ["
Response. Write RS ("message ")
Response. Write "]> </body>"
========================================================== ====

If the mark is plain text, <> & characters cannot be directly stored in XML, which must be escaped. However, this mark does not need to be escaped and these symbols are stored in XML documents.

This prevents unexpected special characters from causing XML parsing errors.

What is the difference between pcdata and CDATA?
========================================================== =====
Pcdata indicates parsed character data.
CDATA is text that is not parsed by the parser. labels in the text are not considered as tags.
CDATA indicates that XML is not parsed. For example, it may be the following section.
<! [CDATA [
If (A> B ){
System. Out. println ();


Note the above ">" symbol.

Pcdata is parsed for the XML parser, so the above> de-resolution will certainly fail, so the object definition should be used. If the above data is expressed as follows using pcdata:

If (A & gt; B ){
System. Out. println ();

CDATA is the keyword used in the XML document to tell the browser that this part of content does not need to be parsed and is used by other programs, such as JavaScript, # pcdata is used in XML constraints. For example, for a DTD-type constraint document, it indicates the content of an element or the value range of an attribute. It is a string,


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