Valid and Well-Formed

XML documents are often described in terms of being

What does this mean and why is it important ?

Xml documents are described as Well-Formed if they conform to the rules of xml

These are the same rules that apply to xhtml documents (after all Xhtml is a special subset of XML)

Xml documents are described as Valid if they conform to the particular specified in the xml file

Both are optional which could result in an xml file being Well-formed but not Valid .