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Filter Chains - Zend_Filter
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:
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.
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: