The Main Differences Between XML and HTML
XML is designed to carry data.
XML describes and focuses on the data while HTML only displays and focuses on how data looks. HTML is all about displaying information but XML is all about describing information. In current scenario XML is the most common tool for data manipulation and data transmission.
XML is used to store data in files and for sharing data between diverse applications. Unlike HTML document where data and display logic are available in the same file, XML hold only data. Different presentation logics could be applied to display the xml data in the required format. XML is the best way to exchange information.
XML is Free and Extensible
XML tags are not predefined. User must "invent" his tags.
The tags used to mark up HTML documents and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard (like <p>, <h1>, etc.).
XML allows the user to define his own tags and document structure.
XML Tags are Case Sensitive
Unlike HTML, XML tags are case sensitive. In HTML the following will work:
|<Message>This is incorrect</message>|
In XML opening and closing tags must therefore be written with the same case:
<message>This is correct</message
XML Elements Must be Properly Nested
Improper nesting of tags makes no sense to XML.
In HTML some elements can be improperly nested within each other like this:
<b><i>This text is bold and italic</b></i>
In XML all elements must be properly nested within each other like this:
<b><i>This text is bold and italic</i></b>
XML is a Complement to HTML
XML is not a replacement for HTML.
It is important to understand that XML is not a replacement for HTML. In Web development it is most likely that XML will be used to describe the data, while HTML will be used to format and display the same data.