XML Syntax Rules

XML Syntax Rules

All XML Elements Must Have a Closing Tag

In HTML, elements do not have to have a closing tag:

<p>This is a paragraph
<p>This is another paragraph

In XML, it is illegal to omit the closing tag. All elements must have a closing tag:
<p>This is a paragraph</p>
<p>This is another paragraph</p>

Note: You might have noticed from the previous example that the XML declaration did not have a closing tag. This is not an error. The declaration is not a part of the XML document itself, and it has no closing tag.

XML Tags are Case Sensitive

XML tags are case sensitive. The tag <Letter> is different from the tag <letter>.

Opening and closing tags must be written with the same case:
<Message>This is incorrect</message>
<message>This is correct</message>

Note: "Opening and closing tags" are often referred to as "Start and end tags". Use whatever you prefer. It is exactly the same thing.

XML Elements Must be Properly Nested

In HTML, you might see improperly nested elements:
<b><i>This text is bold and italic</b></i>

In XML, all elements must be properly nested within each other:
<b><i>This text is bold and italic</i></b>

In the example above, "Properly nested" simply means that since the <i> element is opened inside the <b> element, it must be closed inside the <b> element.

XML Documents Must Have a Root Element

XML documents must contain one element that is the parent of all other elements. This element is called the root element.
<root>
  <child>
    <subchild>.....</subchild>
  </child>
</root>