A strict definition for dark fantasy is difficult to pin down. Gertrude Barrows Bennett has been called "the woman who invented dark fantasy". Both Charles L. Grant and Karl Edward Wagner are credited with having coined the term "dark fantasy"—although both authors were describing different styles of fiction. Brian Stableford argues "dark fantasy" can be usefully defined as subgenre of stories that attempt to "incorporate elements of horror fiction" into the standard formulae of fantasy stories. Stableford also suggests that supernatural horror set primarily in the real world is a form of "contemporary fantasy", whereas supernatural horror set partly or wholly in "secondary worlds" should be described as "dark fantasy".