I’ve been using the Web Developer Accessories since version 5.0 of Internet Explorer. They are very useful. The most used feature is the extra context menu option called “View partial source”. It will provide you with the almost exact source of the selected page fragment. Comes in pretty handy if you generate your HTML on the fly. View Source from the View menu will not help you there, as it returns the downloaded HTML source, not the current (D)HTML of the webpage. never mind the “for IE 5.0“: it also works for IE 5.5 and 6.0+
While you are at it, download and install the Internet Tools for Validating XML and Viewing XSL Output as well. That will allow you to validate your XML data against the registered DTD or XDR Schema (not XSD Schemas, unfortunately) by rightclicking on the XML document when loaded in IE. The XSL Output viewer shows the XML/HTML that is transformed by IE when using the <?xml-stylesheet type=“text/xsl“ href=“…“ ?> processing instruction.