There are some pretty advanced filtering capabilities which a WFS server could advertise;

```xml
<ogc:Filter_Capabilities>
<ogc:Spatial_Capabilities>
<ogc:GeometryOperands>
<ogc:GeometryOperand>gml:Envelope</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Point</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:LineString</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Polygon</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:ArcByCenterPoint</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:CircleByCenterPoint</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Arc</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Circle</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:ArcByBulge</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Bezier</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Clothoid</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:CubicSpline</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Geodesic</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:OffsetCurve</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Triangle</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:PolyhedralSurface</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:TriangulatedSurface</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Tin</ogc:GeometryOperand>
<ogc:GeometryOperand>gml:Solid</ogc:GeometryOperand>
</ogc:GeometryOperands>
<ogc:SpatialOperators>
<ogc:SpatialOperator name="BBOX"/>
<ogc:SpatialOperator name="Equals"/>
<ogc:SpatialOperator name="Disjoint"/>
<ogc:SpatialOperator name="Intersects"/>
<ogc:SpatialOperator name="Touches"/>
<ogc:SpatialOperator name="Crosses"/>
<ogc:SpatialOperator name="Within"/>
<ogc:SpatialOperator name="Contains"/>
<ogc:SpatialOperator name="Overlaps"/>
<ogc:SpatialOperator name="Beyond"/>
</ogc:SpatialOperators>
</ogc:Spatial_Capabilities>
<ogc:Scalar_Capabilities>
<ogc:LogicalOperators/>
<ogc:ComparisonOperators>
<ogc:ComparisonOperator>LessThan</ogc:ComparisonOperator>
<ogc:ComparisonOperator>GreaterThan</ogc:ComparisonOperator>
<ogc:ComparisonOperator>LessThanEqualTo</ogc:ComparisonOperator>
<ogc:ComparisonOperator>GreaterThanEqualTo</ogc:ComparisonOperator>
<ogc:ComparisonOperator>EqualTo</ogc:ComparisonOperator>
<ogc:ComparisonOperator>NotEqualTo</ogc:ComparisonOperator>
<ogc:ComparisonOperator>Like</ogc:ComparisonOperator>
<ogc:ComparisonOperator>Between</ogc:ComparisonOperator>
<ogc:ComparisonOperator>NullCheck</ogc:ComparisonOperator>
</ogc:ComparisonOperators>
<ogc:ArithmeticOperators>
<ogc:SimpleArithmetic/>
<ogc:Functions>
<ogc:FunctionNames>
<ogc:FunctionName nArgs="1">MIN</ogc:FunctionName>
<ogc:FunctionName nArgs="1">MAX</ogc:FunctionName>
<ogc:FunctionName nArgs="1">SIN</ogc:FunctionName>
<ogc:FunctionName nArgs="1">COS</ogc:FunctionName>
<ogc:FunctionName nArgs="1">TAN</ogc:FunctionName>
</ogc:FunctionNames>
</ogc:Functions>
</ogc:ArithmeticOperators>
</ogc:Scalar_Capabilities>
<ogc:Id_Capabilities>
<ogc:EID/>
<ogc:FID/>
</ogc:Id_Capabilities>
</ogc:Filter_Capabilities>
```