>    I am having <sub>P</sub> tag in my xml file i 
> am trying to
> view the contents in the browser. But in browser it is displaying as
> <sub>p</sub> not by displaying subscript of P. 

Of course it is. Someone has carefully escaped the angle brackets to say
"don't treat these as markup, treat them as ordinary "<" and ">"
characters". So that's what the system is doing.

When you are faced with incorrect input like this, disable-output-escaping
can sometimes get you out of the mess. See yesterday's messages on this
list.

Michael Kay
http://www.saxonica.com/