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Writing Filters - Zend_Filter
Zend_Filter supplies a set of commonly needed filters, but developers will often need to write custom filters for their particular use cases. The task of writing a custom filter is facilitated by implementing Zend_Filter_Interface.
Zend_Filter_Interface defines a single method, filter(), that may be implemented by user classes. An object that implements this interface may be added to a filter chain with Zend_Filter::addFilter().
The following example demonstrates how to write a custom filter:
To add an instance of the filter defined above to a filter chain: