 Modifications would also be needed for Russellian, possible-worlds, or Fregean contents of beliefs; and proponents of each of these views have discussed what those might be in the case of belief. (For discussion of indexicals and Russellian contents, see Kaplan 1977, Schiffer 1981, Austin 1990, and the entry on  indexicals;  for discussion of indexicals and possible-worlds content, see Stalnaker 1981; for discussion of indexical beliefs and Fregean contents, see Perry 1977; Evans 1981, McDowell 1984.) It is an open question whether modifications that succeed for the case of belief can also succeed for the case of experience. An influential approach that has been developed for both beliefs and experiences appeals to a special kind of possible world: centered worlds, where these are possible worlds marked with a designated subject and perhaps a designated time or other parameters. The centered-world framework can provide a level of content that can be shared by two perceivers who perceive qualitatively identical but numerically distinct cubes in different locations as being nearby: each experience is true in worlds where there is a cube nearby the designated center of that world. Features such as being nearby the center are called “centering features” (see Egan 2006a, 2006b, 2010), and can be used to describe both the phenomena that indexicals are apt for describing, as well as perceptual constancies and secondary qualities. For discussion see Brogaard 2010 and 2018, Chalmers 2006, Egan 2006a, 2006b, 2010, GReenberg 2018. Centered worlds are implicit in Peacocke’s 1992 discussion of scenario content.