# 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.

## Changing filter chain order

Since 1.10, the `Zend_Filter` chain also supports altering the chain by prepending or appending filters. For example, the next piece of code does exactly the same as the other username filter chain example:

    // Create a filter chain and add filters to the chain
    $filterChain = new Zend_Filter();

    // this filter will be appended to the filter chain
    $filterChain->appendFilter(new Zend_Filter_StringToLower());

    // this filter will be prepended at the beginning of the filter chain.
    $filterChain->prependFilter(new Zend_Filter_Alpha());

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