# Filter Chains

Often multiple filters should be applied to some value in a particular order. For example, a login form accepts a username that should be only lowercase, alphabetic characters. `Zend_Filter` provides a simple method by which filters may be chained together. The following code illustrates how to chain together two filters for the submitted username:

    <// Create a filter chain and add filters to the chain
    $filterChain = new Zend_Filter();
    $filterChain->addFilter(new Zend_Filter_Alpha())
                ->addFilter(new Zend_Filter_StringToLower());

    // Filter the username
    $username = $filterChain->filter($_POST['username']);

Filters are run in the order they were added to `Zend_Filter`. In the above example, the username is first removed of any non-alphabetic characters, and then any uppercase characters are converted to lowercase.

Any object that implements `Zend_Filter_Interface` may be used in a filter chain.