The SQL Server XML data type supports both schema-defined and schema-less XML documents (typed and untyped), and partial documents. Partial documents are still considered well-defined XML, but don’t have surrounding
<?xml>...</xml>tags for example. Either way, the storage engine validates the data when inserting or updating into an
XMLdata type lets us store up to 2GB per column per row, but it’s prudent here to note that just because we can, it doesn’t mean we should.
Click through for the details.