omputation 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>