[Web4lib] XML Editor recommendations?

[Gilman, Mark]

Hi,
 
I'm getting increasingly interested in Keyhole Markup Language (KML),
the XML doctype used by Google Maps and Google Earth and other
applications as well.  
While Google Earth is a pretty good visual editor, I see the necessity
of directly hacking the code.  Opening a KML file in a text editor like
Notepad++ is not very useful,
because text editors tend not to be XML-aware so there's no syntax
highlighting, validation of well-formedness, etc.  
 
Can anyone recommend a good, open-source XML editor? This is my first
real encounter with XML, so I've not much basis upon which to make an
informed choice.
 
Regards,
Mark