trying to validate wfs-t requests using the schemas

Test.java

import org.xml.sax.SAXException;

import javax.xml.XMLConstants;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;
import java.io.IOException;
import java.io.StringReader;
import java.net.URL;

public class Test {

    // taken from the geoserver demo request: WFS_transactionInsert.xml
    private static String tx =
            "<wfs:Transaction service=\"WFS\" version=\"1.0.0\"\n" +
            "  xmlns:wfs=\"http://www.opengis.net/wfs\"\n" +
            "  xmlns:topp=\"http://www.openplans.org/topp\"\n" +
            "  xmlns:gml=\"http://www.opengis.net/gml\"\n" +
            "  xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"\n" +
            "  xsi:schemaLocation=\"http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.0.0/WFS-transaction.xsd http://www.openplans.org/topp http://localhost:8080/geoserver/wfs/DescribeFeatureType?typename=topp:tasmania_roads\">\n" +
            "  <wfs:Insert>\n" +
            "    <topp:tasmania_roads>\n" +
            "      <topp:the_geom>\n" +
            "        <gml:MultiLineString srsName=\"http://www.opengis.net/gml/srs/epsg.xml#4326\">\n" +
            "          <gml:lineStringMember>\n" +
            "            <gml:LineString>\n" +
            "              <gml:coordinates decimal=\".\" cs=\",\" ts=\" \">\n" +
            "494475.71056415,5433016.8189323 494982.70115662,5435041.95096618\n" +
            "              </gml:coordinates>\n" +
            "            </gml:LineString>\n" +
            "          </gml:lineStringMember>\n" +
            "        </gml:MultiLineString>\n" +
            "      </topp:the_geom>\n" +
            "      <topp:TYPE>alley</topp:TYPE>\n" +
            "    </topp:tasmania_roads>\n" +
            "  </wfs:Insert>\n" +
            "</wfs:Transaction>";


    public static void main(String[] args) {
        try {
            validateWFST(tx);
            System.out.println("Schema was valid!");
        }
        catch (SAXException | IOException e) {
            System.out.println("Schema was invalid b/c " + e.toString());
        }
    }

    private static void validateWFST(String transaction) throws IOException, SAXException {
        SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
        Schema schema = factory.newSchema(new URL("http://schemas.opengis.net/wfs/1.0.0/wfs.xsd"));
        Validator validator = schema.newValidator();
        validator.validate(new StreamSource(new StringReader(transaction)));
        // why does the validation fail?
        // Schema was invalid b/c org.xml.sax.SAXParseException; lineNumber: 8; columnNumber: 26; cvc-complex-type.2.4.a: Invalid content was found starting with element 'topp:tasmania_roads'. One of '{"http://www.opengis.net/gml":_Feature}' is expected.
    }
}