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  // Copyright 2006, 2007, 2008, 2009 The Apache Software Foundation
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 package org.apache.tapestry5.annotations;
 import static java.lang.annotation.ElementType.FIELD;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
 import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;

Annotation placed on a field to indicate that it is, in fact, a component parameter. Parameters may be optional or required. Required parameters must be bound.
 public @interface Parameter

The name of the parameter. If not specified, the name of the parameter is derived from the name of the field (after stripping off leading and trailing punctuation).
     String name() default "";

If true, the parameter is required and and must be bound. If false (the default), then the parameter is optional.
     boolean required() default false;

If false, and the parameter is bound, then the value for the parameter must not be null. The default is true, to allow nulls. This is different than required, in that the parameter may be bound, but bound to a null value.
     boolean allowNull() default true;

If true (the default), then the value for the parameter is cached while the component is, itself, rendering. Values from invariant bindings (such as literal strings) are always cached, regardless of this setting. Set this attribute to false to force the parameter to be re-read every time the field is accessed, even while the component is rendering.
     boolean cache() default true;

The default value for the parameter if not bound (and not the empty string). This is a binding expression, typically the name of a property of the component to bind.
     String value() default "";

The default binding prefix for the parameter, if no specific binding prefix is provided with the binding. There is rarely a reason to override this. Typically, non-standard default binding prefixes are paired with specific implementations, and used with parameters whose name reflects the binding prefix.

See also:
     String defaultPrefix() default .;

Used to mark a parameter as requiring earlier initialization than other parameters. This is used when default bindings for secondary parameters rely on a principal parameter, which itself may have a default value. This ensures that the binding for the principal parameter(s) are initialized, possibly involving a defaulter method, before the secondary parameters are initialized (as they may need to know if the principal parameter is bound, and what type of value it is bound to). This is rarely used, and it is highly unlikely a single component would have more than a single principal parameter.
     boolean principal() default false;

Used to create a default binding, connecting the parameter to a property of the container whose property name matches the id of the component. This is frequently used for form element components. This default binding is only used if there is no matching container property.

See also:, org.apache.tapestry5.ComponentResources)
    boolean autoconnect() default false;
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