XML is not a replacement for HTML.
XML and HTML were designed with different goals:
HTML is about displaying information, while XML is about carrying information.
User definable tags
Defined set of tags designed for web display
End tags required for well formed documents
End tags not required
Quotes required around attributes values
Quotes not required
Slash required in empty tags
Slash not required
XML is used in many aspects of web development, often to simplify data storage and sharing.
XML Separates Data from HTML
If you need to display dynamic data in your HTML document, it will take a lot of work to edit the HTML each time the data changes.
With XML, data can be stored in separate XML files. This way you can concentrate on using HTML for layout and display, and be sure that changes in the underlying data will not require any changes to the HTML.
XML Simplifies Data Sharing
In the real world, computer systems and databases contain data in incompatible formats.
XML data is stored in plain text format. This provides a software- and hardware-independent way of storing data.
This makes it much easier to create data that can be shared by different applications.
XML Simplifies Data Transport
One of the most time-consuming challenges for developers is to exchange data between incompatible systems over the Internet.
Exchanging data as XML greatly reduces this complexity, since the data can be read by different incompatible applications.
XML Simplifies Platform Changes
Upgrading to new systems (hardware or software platforms), is always time consuming. Large amounts of data must be converted and incompatible data is often lost.
XML data is stored in text format. This makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing data.
XML Makes Your Data More Available
Different applications can access your data, not only in HTML pages, but also from XML data sources.
With XML, your data can be available to all kinds of "reading machines" (Handheld computers, voice machines, news feeds, etc), and make it more available for blind people, or people with other disabilities.
XML is Used to Create New Internet Languages
A lot of new Internet languages are created with XML.
Here are some examples:
If Developers Have Sense
If they DO have sense, future applications will exchange their data in XML.
The future might give us word processors, spreadsheet applications and databases that can read each other's data in XML format, without any conversion utilities in between.
XML is verbose and it can be 4-6 times larger in size compared to a csv or a tab delimited file. If your network lacked bandwidth and/or your content is too large and network throughput is vital to the application then you may consider using a csv or tab delimited format instead of an XML.