*
 * <td>Minimum legal value for an attribute or parameter.  See
 * {@link javax.management.openmbean}.</td>
 *
 * <tr><td><a name="mxbean"><i>mxbean</i></a><td>String</td>
 * <td>MBeanInfo</td>
 *
 * <td>The string {@code "true"} or {@code "false"} according as this
 * MBean is an {@link MXBean}.  A Standard MBean or MXBean registered
 * directly with the MBean Server or created using the {@link
 * StandardMBean} class will have this field in its MBeanInfo
 * Descriptor.</td>
 *
 * <tr><td><a name="openType"><i>openType</i></a><td>{@link OpenType}</td>
 * <td>MBeanAttributeInfo<br>MBeanOperationInfo<br>MBeanParameterInfo</td>
 *
 * <td><p>The Open Type of this element.  In the case of {@code
 * MBeanAttributeInfo} and {@code MBeanParameterInfo}, this is the
 * Open Type of the attribute or parameter.  In the case of {@code
 * MBeanOperationInfo}, it is the Open Type of the return value.  This
 * field is set in the Descriptor for all instances of {@link
 * OpenMBeanAttributeInfoSupport}, {@link
 * OpenMBeanOperationInfoSupport}, and {@link
 * OpenMBeanParameterInfoSupport}.  It is also set for attributes,
 * operations, and parameters of MXBeans.</p>
 *
 * <p>This field can be set for an {@code MBeanNotificationInfo}, in
 * which case it indicates the Open Type that the {@link
 * Notification#getUserData() user data} will have.</td>
 *
 * <tr><td><a name="originalType"><i>originalType</i></a><td>String</td>
 * <td>MBeanAttributeInfo<br>MBeanOperationInfo<br>MBeanParameterInfo</td>
 *
 * <td><p>The original Java type of this element as it appeared in the
 * {@link MXBean} interface method that produced this {@code
 * MBeanAttributeInfo} (etc).  For example, a method<br> <code>public
 * </code> {@link MemoryUsage}<code> getHeapMemoryUsage();</code><br>
 * in an MXBean interface defines an attribute called {@code
 * HeapMemoryUsage} of type {@link CompositeData}.  The {@code
 * originalType} field in the Descriptor for this attribute will have
 * the value {@code "java.lang.management.MemoryUsage"}.
 *
 * <p>The format of this string is described in the section <a
 * href="MXBean.html#type-names">Type Names</a> of the MXBean
 * specification.</p>
 *
 * <tr><td>severity</td><td>String<br>Integer</td>
 * <td>MBeanNotificationInfo</td>
 *
 * <td>The severity of this notification.  It can be 0 to mean
 * unknown severity or a value from 1 to 6 representing decreasing
 * levels of severity.  It can be represented as a decimal string or
 * an {@code Integer}.</td>
 *
 * <tr><td>since</td><td>String</td><td>Any</td>
 *
 * <td>The version of the information model in which this element
 * was introduced.  A set of MBeans defined by an application is
 * collectively called an <em>information model</em>.  The
 * application may also define versions of this model, and use the
 * {@code "since"} field to record the version in which an element
 * first appeared.</td>
 *
 * <tr><td>units</td><td>String</td>
 * <td>MBeanAttributeInfo<br>MBeanParameterInfo<br>MBeanOperationInfo</td>
 *
 * <td>The units in which an attribute, parameter, or operation return
 * value is measured, for example {@code "bytes"} or {@code
 * "seconds"}.</td>
 *
 * </table>
 *
 * <p>Some additional fields are defined by Model MBeans.  See
 * {@link javax.management.modelmbean.ModelMBeanInfo ModelMBeanInfo}
 * and related classes and the chapter "Model MBeans" of the
 * <a href="http://java.sun.com/products/JavaManagement/download.html">
 * JMX Specification</a>.</p>
 *
 * @since 1.5
 */
public interface Descriptor extends Serializable, Cloneable
{

    /**
     * Returns the value for a specific field name, or null if no value
     * is present for that name.
     *
     * @param fieldName the field name.
     *
     * @return the corresponding value, or null if the field is not present.
     *
     * @exception RuntimeOperationsException if the field name is illegal.
     */
    public Object getFieldValue(String fieldName)
            throws RuntimeOperationsException;

    /**
     * <p>Sets the value for a specific field name. This will
     * modify an existing field or add a new field.</p>
     *