Wow, tbarak himself answered the question, so take his advice as godspell.
Without having lots of knowledge about XML, accept my humble opinion boosted by a small search I've made:
The Crimson Editor is just one, but bear some more info in mind...
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XML is Text-based
XML is a text-based markup language.
One great thing about XML is that XML files can be created and edited using a simple text-editor like Notepad.
However, when you start working with XML, you will soon find that it is better to edit XML documents using a professional XML editor.
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Why Not Notepad?
Many web developers use Notepad to edit both HTML and XML documents because Notepad is included with the most common OS and it is simple to use. Personally I often use Notepad for quick editing of simple HTML, CSS, and XML files.
But, if you use Notepad for XML editing, you will soon run into problems.
Notepad does not know that you are writing XML, so it will not be able to assist you.
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Why an XML Editor?
Today XML is an important technology, and development projects use XML-based technologies like:
XML Schema to define XML structures and data types
XSLT to transform XML data
SOAP to exchange XML data between applications
WSDL to describe web services
RDF to describe web resources
XPath and XQuery to access XML data
SMIL to define graphics
To be able to write error-free XML documents, you will need an intelligent XML editor!
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XML Editors
Professional XML editors will help you to write error-free XML documents, validate your XML against a DTD or a schema, and force you to stick to a valid XML structure.
An XML editor should be able to:
Add closing tags to your opening tags automatically
Force you to write valid XML
Verify your XML against a DTD
Verify your XML against a Schema
Color code your XML syntax
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Altova's XMLSPY
At W3Schools we have been using XMLSPY for many years. XMLSPY is our favorite XML editor. These are some of the features we especially like:
Easy to use
Syntax coloring
Automatic tag completion
Automatic well-formed check
Easy switching between text view and grid view
Built in DTD and / or Schema validation
Built in graphical XML Schema designer
Powerful conversion utilities
Database import and export
Built in templates for most XML document types
Built in XPath analyzer
Full SOAP and WSDL capabilities
Powerful project management
hope I've helped with my humble opinion.
regards
the Elder
"imagination is more important than knowledge."
Albert Einstein