SVG 1.1 introduced the enable-background property. The property defined the back drop under the filter region at the time that the <filter> element was invoked. The concept defined by this property was identified to be incompatible with the model of stacking context in CSS at the time writing this specification. UAs can choose to implement the enable-background property as defined in SVG 1.1 but will not be compatible to this specification or to CSS Compositing and Blending [W3C Working Draft].