This can happen if the XSD schema file referenced is itself not valid or if it cannot be found.
MSXML can also be configured to use a cached schema instead and ignore the schema file referenced in this value.
The mechanism for associating an XML document with a schema varies according to the schema language.
The association may be achieved via markup within the XML document itself, or via some external means.
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Two more expressive XML schema languages in widespread use are XML Schema (with a capital S) and RELAX NG.
This validator tries to check these as well, which makes its results much more applicable to real-world applications: namespaces in .
An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself.
XSD files are "XML Schemas" that describe the structure of a XML document.
The validator checks for well formedness first, meaning that your XML file must be parsable using a DOM/SAX parser, and only then does it validate your XML against the XML Schema.