Going to Window->Preferences->Rinzo XML you will find the configuration settings for this editor.
The most important ones are the:

  • Syntax coloring.
  • Templates configuration.
  • Indentation using tag or space.
  • Whether formatting should be executed before each save operation
  • Change editor's background.
  • Java Integration.

Unless a more specialized editor like ant editor for build.xml file exists, this editor will be used to open the following extensions: .xml, xsd, tld, xsl, xslt, wsdl, exsd and xmi.
If you want to associate it with other extensions you can do it in Window->Preferences->General->File Associations