<?php
    /** 
     * AbstractColleague. 
     */ 
    interface Filter 
    { 
 public function filter($value); 
    } 

    /** 
     * Colleague. We decide in the implementation phase 
     * that Colleagues should not know the next Colleague 
     * in the chain, resorting to a Mediator to link them together. 
     * This choice succesfully avoids a base abstract class 
     * for Filters. 
     * Remember that this is an example: it is not only 
     * Chain of Responsibility that can be alternatively implemented 
     * as a Mediator. 
     */ 
    class TrimFilter implements Filter 
    { 
  public function filter($value) 
  { 
      return trim($value); 
  } 
    } <PRE class=php name="code">    /** 
     * Colleague. 
     */ 
    class NullFilter implements Filter 
    { 
 public function filter($value) 
 { 
     return $value ? $value : ''; 
 } 
    } 

    /** 
     * Colleague. 
     */ 
    class HtmlEntitiesFilter implements Filter 
    { 
 public function filter($value) 
 { 
     return htmlentities($value); 
 } 
    }
</PRE><PRE class=php name="code">    /** 
     * The Mediator. We avoid referencing it from ConcreteColleagues 
     * and so the need for an interface. We leave the implementation 
     * of a bidirectional channel for the Observer pattern's example. 
     * This class responsibility is to store the value and coordinate 
     * filters computation when they have to be applied to the value. 
     * Filtering responsibilities are obviously a concern of 
     * the Colleagues, which are Filter implementations. 
     */ 
    class InputElement 
    { 
 protected $_filters; 
 protected $_value; 

 public function addFilter(Filter $filter) 
 { 
     $this->_filters[] = $filter; 
     return $this; 
 } 

 public function setValue($value) 
 { 
     $this->_value = $this->_filter($value); 
 } 

 protected function _filter($value) 
 { 
     foreach ($this->_filters as $filter) { 
  $value = $filter->filter($value); 
     } 
     return $value; 
 } 

 public function getValue() 
 { 
     return $this->_value; 
 }   
    } 

    $input = new InputElement(); 
    $input->addFilter(new NullFilter()) 
   ->addFilter(new TrimFilter()) 
   ->addFilter(new HtmlEntitiesFilter()); 
    $input->setValue(' You should use the <h1>-<h6> tags for your headings.'); 
    echo $input->getValue(), "\n";
</PRE>
<PRE></PRE>