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package javax.faces.view.facelets;


/**
 * The root class of the abstraction that
 * dictates how attributes on a markup element in a Facelets VDL page
 * are wired to the JSF API object instance associated with that
 * element.  The single method on this interface, {@link #applyRule},
 * returns an encapsulation of the behavior that actually does the work
 * of handling the attribute and its value.  There are implementations of
 * specific concrete subclasses of this class for all the basic kinds of
 * elements that appear in Facelets VDL pages: components,
 * non-components, and attached objects.
 *
 * 

 * For example, consider this markup:

<h:inputText value="#{user.userid}" 
                valueChangeListener="#{user.newUserId}" />

 * Two MetaRule instances are involved in this example.

 * 
 *
 * The first has
 * an applyRule() method that returns a {@link Metadata}
 * instance that, when its applyMetada() method is called,
 * dictates how the "value" attribute is processed: calling {@link
 * javax.faces.component.UIComponent#setValueExpression} on the
 * UIComponent instance associated with the
 * <h:inputText> element.

 * The second has an applyRule() method that returns
 * a {@link Metadata} instance that, when its
 * applyMetadata() method is called, dictates how the
 * "valueChangeListener" attribute is processed: calling {@link
 * javax.faces.component.EditableValueHolder#addValueChangeListener}.

 * 

 * 
 *
 * @since 2.0
 */
public abstract class MetaRule {

    
    /**
     * Return an abstraction that takes
     * appropriate action given the kind of rule represented by the
     * argument name, in the context of this particular
     * concrete subclass of MetaRule.  The abstraction must
     * encapsulate the value from the argument
     * attribute.
     * @since 2.0
     * @param name the name for this rule.  This will generally be the
     * name of a tag attribute in the VDL.
     * @param attribute the name/value pair for this attribute on this
     * particular instance of an element in the page.
     * @param meta the MetadataTarged that can be used to
     * discern what kind of action to encapsulate within the abstraction
     * to be returned.

     */
    public abstract Metadata applyRule(String name, TagAttribute attribute,
            MetadataTarget meta);

}