Filters:
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$Id: filters.txt 2 2004-02-29 18:58:13Z schst $

Filters can be used to modify the value while it is sent to
the end user or when the end user sends a value to the form.

Filters are objects that supply at least the following three methods:

1. integer patForms_Filter::getType()
Returns the type of the filter, either PATFORMS_FILTER_TYPE_HTTP
or PATFORMS_FILTER_TYPE_PHP.
If a filter is of type HTTP, it is located between the patForms_Element
object and the browser of the user, that means the value will be filtered
directly when it has been submitted.

If a filter is of type PHP, it is located between the patForms_Element
and the PHP script you developed. That means after the form is submitted,
the value will be validated and only filtered, when you call
patForms_Element::getValue()

2. mixed in( mixed value )
This method is called when data is pushed to the patForms_Element object.
For PHP filters this is when you call patForms_Element::setValue(), or when
you have set a default value.
For HTTP filters, it is called when the user submitted data to the form.

3. mixed out( mixed value )
This method is called when data is pulled from the patForms_Element object.
For PHP filters this is when you call patForms_Element::getValue().
For HTTP filters, it is invoked when the form element is generated.

The easiest way to create a custom filter is to derive it from patForms_Filter.