modern myth, e.g.:
Alice in Wonderland;
Rip Van Winkle;
Having become part of the general cultural background, such modern myths are referred to by other fictional characters who, like us, regard them as fictional characters. Thus, in SM Stirling's Against The Tide Of Years, one character quotes Spock from Star Trek and another mentions Yoda from Star Wars. Against the Tide Of Years is set in the timeline of Stirling's Nantucket Trilogy, not of either Star Trek or Star Wars. However, Stirling's time travelers began their lives in a twentieth century which, until the mysterious Event, was indistinguishable from ours.
In Poul Anderson's The Corridors Of Time, Malcolm Lockridge is astounded when his companion does not recognize the name "James Bond" but soon learns that she is a time traveler from a later period. Anderson's Time Patrolman Manse Everard refers to "'...real Sherlock Holmes work...'" (Time Patrol, p. 529) in circumstances that are consistent with Holmes being a widely known fictional detective, as we would expect. However, the Time Patrol timeline contains an unnamed "'...private inquiry agent...'" (p. 21) who exactly fits the description of Sherlock Holmes. Anderson is playing with the idea that a fictional character (Holmes) might be not fictional but real to other fictional characters (the Time Patrolmen).
Finally, in a certain kind of imaginary multiverse, what is fictional in one universe is real in another. Thus, two men answering the descriptions of Holmes and Watson show up at Anderson's inter-cosmic inn, the Old Phoenix. And Anderson seems yet again to have covered every possibility: the real, the fictitious and the ambiguous.
Poul Anderson, "Star of the Sea" IN Anderson, Time Patrol (New York, 2006), pp. 467-640 AT section 6, p. 529.
Poul Anderson, "Time Patrol" IN op. cit., pp. 1-53 AT section 3, p. 21.