Do you mean render element? I might be able to add this. Somewhat counter to intuition, some pixels will have negative values. This is because it redistributes energy from bright pixels to dark pixels (just like a blur does), therefore the brighter pixels become less bright, so for an "additive workflow" the render element will be negative in those areas. Thankfully, EXR and Nuke eat this stuff for breakfast (but not all tools do).
EDIT: If you are using compositing software that doesn't like negative values, clamping at 0 would be visually OK, but wouldn't reproduce the beauty element 100%.