On the meaning of XML file format in the framework

1. XML The label must be customized , But when writing a signature, it must have meaning  
     Labels cannot be cross coded  
     Special characters require entity escape

2. XML There must be a root node , That is, other labels are covered  

Spring For the <Beans>      pom For the <project>

3. XML There should also be a header statement   It is not a hard requirement , But it covers the coding format , It is necessary to define , It is also generally defined
    <?xml version="1.0" encoding="UTF-8"?>

4. XML Should also be constrained , There are two kinds of constraint files DTD and XSD     They can all be introduced from the network and locally
    When we use the framework , Frames have specific tags to be recognized by the frame , So write it yourself xml To identify the needs of the framework, we need to introduce constraints
    XSD The introduction of :
    < Root tag xmls:xsi="w3c Constraint address "
           xsi:schemaLocation=" The address of the frame constraint "
           <!-- After the above two are completed, the introduction is actually completed , But when we use labels, we also need to add the address of frame constraint in front of each label, which is very troublesome -->
           <!-- Therefore, by introducing a unified label prefix, you can write directly without paying attention to the prefix -->
           xmlns=" Frame constraint address "
    >
    We usually use Spring etc. xml The writing method is carried out through such constraints