Dynamic filter in UWL

Hi everybody,

is it possible to create a filter for UWL with dynamic values? For example I want to build a filter, which proves whether the subject contains the username (of the current logged in portaluser) or not. I tried this, but it doesn’t work:

<AllowedFilters>

<CompoundExpression logicalOperation="OR" defaultViewFilter="no">

<Expression name="subject" value="{$UserName}" comparator="Contains"/>

<Descriptions default="Subject-User Filter"/>

</CompoundExpression>

</AllowedFilters>

The filter only takes the value as a string and not as a variable. Any ideas what's wrong or is it just not possible?

Thanks for help in advance

Konrad