Adding custom filters in plans

Hello,

Has anyone an idea of where I can find some docs on how to define filters in the planModes? One of the things I try to do for example is to add a filter to hide all items except for stories and defect to use as my release notes view.

I'm able to add a custom filter but I cannor configure it.
Where can I find info which filter it can implement or what parameters to pass.

<configuration-data xmlns="http://com.ibm.team.apt.configuration/planConfigurationElement" id="com.ibm.team.apt.configuration.planConfigurationElement">

			    <filter id="my.apt.common.ui.filter.test" implementation="com.ibm.team.apt.internal.ui.filter.NullValueFilter" name="myFilter">

			    	<parameters>

					      <parameter key="field" value="com.ibm.team.apt.attribute.planitem.priority"/>

					</parameters> 

			    </filter>

			    <groupmode id="_rWIXsCtxEd-r3IqQQDxJFA" implementation="com.ibm.team.apt.internal.ui.structure.EnumerationGroupProvider" name="Project">

			        <parameters>

			            <parameter key="attribute" value="com.ibm.team.apt.attributes._Project"/>

			        </parameters>

			    </groupmode>

			    <sortmode id="_d9GwsF28Ed-Qv5E7tXsh_Q" implementation="com.ibm.team.apt.internal.ui.sortmode.GenericPlanItemSorter" name="Project">

			        <parameters>

			            <parameter key="attribute" value="com.ibm.team.apt.attributes._Project"/>

			        </parameters>

			    </sortmode>

</configuration-data>

Thanks