AS XML is a format used primarily to store data, I would be surprised to see that RoboHelp did the slightest bit to help with your goal. Likely it's not going to interpret XML as a topic and allow formatting as it would if the file were an HTM file.
It's my own understanding (which is possibly flawed) that the ability to import and export XML is based on either importing XML to use to create HTM pages for topics, or to take a collection of HTM topics and export them out for repurposing in a different system.
I'll have to leave it at this point and we can hope someone else that has more experience on this aspect will pop in to advise. Perhaps Willam van Weelden?
Rick is right.
Since XML files store data using a tag-based structure, those tags can be anything you want them to be. So browsers won't know what to do with them.
You will need to convert the tags to those recognized by a browser. Here's a reference of supported tags:
There might be some free Internet tools or utilities that can convert xml into html output. You probably just have to link up the tags in the xml file with the desired html tag.
Alternately, you could do a find and replace on the xml file using a text editor (notepad++ s a good one) once you determine the final tags in your output file.