The syntax rules of XML are very simple and logical. The rules are easy to learn, and easy to use.
All XML Elements Must Have a Closing Tag
In HTML, you will often see elements that don't have a closing tag:
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In XML, it is illegal to omit the closing tag. All elements must have a closing tag:
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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 elements are defined using XML tags.
XML tags are case sensitive. With XML, the tag
Opening and closing tags must be written with the same case:
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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 will often see improperly nested elements:
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In XML, all elements must be properly nested within each other:
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In the example above, "Properly nested" simply means that since the element is opened inside the element, it must be closed inside the 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.
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XML Attribute Values Must be Quoted
XML elements can have attributes in name/value pairs just like in HTML.
In XML the attribute value must always be quoted. Study the two XML documents below. The first one is incorrect, the second is correct:
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The error in the first document is that the date attribute in the note element is not quoted.
Comments in XML
The syntax for writing comments in XML is similar to that of HTML.
With XML, White Space is Preserved
HTML reduces multiple white space characters to a single white space:
| HTML: | Hello my name is Tove |
| Output: | Hello my name is Tove. |
With XML, the white space in your document is not truncated.
XML Stores New Line as LF
In Windows applications, a new line is normally stored as a pair of characters: carriage return (CR) and line feed (LF). The character pair bears some resemblance to the typewriter actions of setting a new line. In Unix applications, a new line is normally stored as a LF character. Macintosh applications use only a CR character to store a new line.
