BUR #5845 has been rejected.
create alias soft_focus -> depth_of_field
It's an effect utilizing depth_of_field to direct the viewer's gaze to one part of the image.
Alternatively, it could also be aliased to depth_of_field instead, but it seems to be commonly used by artists (although undertagged).
Edit: I changed it from an implication to an alias since after doing a bit more research and looking at more examples within and outside of Danbooru, it's practically depth_of_field. The statue example for soft_focus in its Wikipedia article is just blurry_background, and I found this tag by accident while looking for another tag, so it makes sense to go with the alias.
Updated by yyflandre