Before a schema can be added to an System.Xml.Schema.XmlSchemaSet, it has to be successfully preprocessed. Preprocessing performs the following basic tasks.

If the XmlSchemaSet.IsCompiled property of the System.Xml.Schema.XmlSchemaSet to add is true, all schemas in the System.Xml.Schema.XmlSchemaSet to add are added to the System.Xml.Schema.XmlSchemaSet. If the XmlSchemaSet.IsCompiled property of the System.Xml.Schema.XmlSchemaSet to add is false, each schema added is preprocessed before being added. If any of the schemas in the newly added System.Xml.Schema.XmlSchemaSet fails to be preprocessed, no schemas are added; instead, an System.Xml.Schema.XmlSchemaException is thrown. As a result, the following two code example are not equivalent.

' First example
schemaSet.Add(schemaSet1)

' Second example
Dim schema As XmlSchema

For Each schema in schemaSet.Schemas()

    schemaSet.Add(schema)

Next

// First example
schemaSet.Add(schemaSet1);

// Second example
foreach(XmlSchema schema in schemaSet.Schemas())
{
    schemaSet.Add(schema);
}

The previous two code examples are not equivalent. In the first example, if an invalid schema exists in schemaSet1 and its XmlSchemaSet.IsCompiled property is set to false, no schemas are added to schemaSet. In the second example, a number of schemas can be added to schemaSet before an invalid schema is encountered and an exception is thrown.