In that case if you're looking for a dedicated, fully featured and powerful XML editor that can be used in Ubuntu Linux, then you should try the award winning utility called XML Copy Editor.
*. Syntax highlighting.
*. Check for spellings and styles.
*. Show/Hide attributes.
*. Insert: Symbols, elements, entity, etc.
*. Wrap words, folding.
*. Enable/Disable element pane.
*. Find and replace.
*. Excellent dedicated "XML" printing (pretty-print): With, wrapped long lines and highlighted codes, etc.
*. Export the XML files to PDF.
*. Word count and enter commands.
*. Check for well-formedness.
*. Validation DTD, XML Schema, Relax NG, Schematron, etc... are just a few of its main features to mention.
You can install XML Copy Editor in Ubuntu 11.04 Natty Narwhal, 11.10, 10.10 and 10.04 by using the below command.
sudo apt-get install xmlcopyeditorThat should do it.