Having this filter definition established provides the foundation
for Zend_Filter_Interface, which requires a single
method named filter() to be implemented by a filter
class.
Following is a basic example of using a filter upon two input data, the ampersand (&) and double quote (") characters:
<?php
$htmlEntities = new Zend_Filter_HtmlEntities();
echo $htmlEntities->filter('&'); // &
echo $htmlEntities->filter('"'); // "