Is xmlns:xsi=“http://www.w3.org/2001/XMLSchema-instance” a special case in XML?

Question

When we use a namespace, we should also indicate where its associated XSD is located at, as can be seen in the following example:

Answer 1

There are four built in declarations for Xml schemata; type, nil, schemaLocation and noNamespaceSchemaLocation as are "present in every schema by definition." You can read about them in the Xml Schema recommendation.