What factors will determine the extent of a defendant's obligation to prevent the injury of a third person as a result of their witness witnessing an accident?

"The evaluation of these factors will indicate the degree of the defendant's foreseeability: obviously defendant is more likely to foresee that a mother who observes an accident affecting her child will suffer harm than to foretell that a stranger witness will do so. Similarly, the degree of foreseeability of the third person's injury is far greater in the case of his contemporaneous observance of the accident than that in which he subsequently learns of it. The defendant is more likely to foresee that shock to the nearby, witnessing mother will cause physical harm than to anticipate that someone distant from the accident will suffer more than a temporary emotional reaction. All these elements, of course, shade into each other; the fixing of obligation, intimately tied into the facts, depends upon each case." (Dillon v. Legg, supra, 68 Cal.2d at pp. 740-741, 69 Cal.Rptr. 72, 441 P.2d 912.)