XML | Syntax

Prerequisite: XML | Basics In this article, we are going to discuss XML syntax rule which is used while writing an XML document or an XML application. It is a very simple and straight forward to learn and code. Below is a complete XML document to discuss each component in detail. 

<?xml version="1.0" encoding="UTF-8"?>
<message>
   <to>Students</to>
   <from>Teacher</from>
   <subject>Regarding assignment submission</subject>
   <text>All students will have to submit assignment by tomorrow.</text>
</message>

Syntax rules for XML declaration or XML Prolog: 

<?xml version="1.0" encoding="UTF-8"?>

Below is the explanation of each point.

• This line is called XML Prolog or XML declaration.
• This line is optional i.e, it can be either used or not in an XML document. However, it should be the very first line if used.
• The version="1.0" is the version of the XML currently used. There are various versions of XML available.
• The encoding="UTF-8" specifies the character encoding used while writing an XML document, for example, êèé is for French and so on. Its default value is "UTF-8". For more about character encoding click here.
• This declaration is case sensitive for example "xml" should be in lower case in .

Syntax rules for Root Element:

• Every XML files should have one or more Root elements to avoid error. For example below code is wrong because it's not containing Root element. 

   <to>Students</to>
   <from>Teacher</from>
   <subject>Regarding assignment submission</subject>
   <text>All students will have to submit assignment by tomorrow.</text>

• In the first example the Root element is <message> and all the remaining elements <to>, <from> etc is the child element and reside within the root element.
• It is case sensitive.
• The XML element should have a closing element for example <text category = "message">Hi</text> is correct but <text category = "message">Hi is not correct because it does not contain the closing element and it will throw an error and vice-versa.
• The elements in XML should be nested properly otherwise it will throw an error. For example <to><from>Geeks</from></to> is nested correctly but <to><from>Geeks</to></from> is wrong because if <from> is opened inside the <to> element then this should also end inside of the </to> element.
• It is also case sensitive i.e, the starting and closing element should be in the same case. For example <to>....</to> is correct but <to>.....</To> is not correct and it will throw an error.
• The XML attribute is having two part one is Name and other is its value. It resides inside of the opening of an XML element. For example: <text category = "message">All students will have to submit the assignment by tomorrow.</text> Here category is the attribute name and message is its value and the attribute value should either be in a single quotation or in double quotation otherwise it will throw an error. The Attribute Name is written without any quotation.
• The XML attribute is also case sensitive.
• An XML element can have multiple attributes but can not have the same attribute names in the same element. For example: <text category ="message" purpose = "greet">GeeksforGeeks</text> Above attributes is correct because of having multiple attributes with the different attribute name. <text category ="message" category = "greet">GeeksforGeeks</text> Above attribute is wrong because of having the same attribute name in a single element.

XML Comments: Correct syntax for writing XML comments are: <!– It is comment section –>
Incorrect comments: <!– It is comment — section –> i.e. Two dashes in between the comment is not allowed.