and escape characters -- study0424

The content contained by <![CDATA[]]> this tag will be represented as plain text , i.e. <![CDATA[<]]> text content “<” . 
　　This tag is used in xml documents, let's take a look at the use of escape characters. We know that in xml, characters such as ”<” , ”>” , ”&” etc. cannot be stored directly, otherwise an error will be reported during the xml syntax check . If you want to use these symbols in xml, you must escape them as entities, such as ”<” , ”>” , ”&” , so that you can save them into the xml document. 
　　When read by the program, the parser will automatically convert these entities back to ”<” , ”>” , ”&” . For example:  　　The above writing method will report an error, it should be written like this :  　　It is worth noting that:  　　(1) There must be no spaces between escape sequence characters;  　　(2) The escape sequence must end with ";";  　　(3) Separate The occurrence of "&" is not considered to be the beginning of an escape;  　　(4) case-sensitive. 　　In XML, the characters that need to be escaped are:  　　(1)&　　　　　(2)<　　　　　(3)>　　　　　(4)"　　　　　(5)'　　　　　But strictly speaking, only "<" and "&" are illegal in XML , the other three can exist legally, but it is a good practice to escape them all. 
　　 <age> age < 30 </age>  

　　 <age> age &lt; 30 </age>  





　　 

&amp;  
&lt;  
&gt;  
&quot;  
&apos;  

　　In any case, the characters before escaping and the characters after escaping will be parsed by the xml parser. For convenience , it is used <![CDATA[]]> to include content that is not parsed by the xml parser. But it should be noted that: 
　　(1) This part cannot contain any more ”]]>” ; 
　　(2) Nesting is not allowed; 
　　(3) ”]]>” This part cannot contain spaces or newlines. 
　　Finally, let's talk about <![CDATA[]]> the relationship with xml transfer characters. Does the two seem to have duplicate functions? 
　　Yes, their functions are the same, but the application scenarios and requirements are slightly different: 
　　(1) It is <![CDATA[]]> not applicable to all situations, but escape characters are OK; 
　　(2) <![CDATA[]]> It is verbose for short strings, and for long strings, escape characters are written. It is less readable; 
　　(3)  <![CDATA[]]> means that the xml parser ignores parsing, so it is faster.