Create a new SchemaValidator, which may be used for validating instance
documents.
The SchemaValidator uses the cache of schema components held by the
SchemaManager. It may also add new components to this cache (for example,
when the instance document references a schema using xsi:schemaLocation).
It is also affected by changes to the schema cache that occur after the
SchemaValidator is created.
When schema components are used for validating instance documents (or for compiling
schema-aware queries and stylesheets) they are sealed to prevent subsequent modification.
The modifications disallowed once a component is sealed include adding to the substitution group
of an element declaration, adding subtypes derived by extension to an existing complex type, and
use of <xs:redefine>