42. The method according to claim 39 , wherein the first and the second content areas display content of different first and second content categories, respectively, and wherein: if the indication is of dropping the first element into the second content area, the third content items are of the second content category of the second content area, and if the indication is of dropping the second element into the first content area, the fourth content items are of the first content category of the first content area.
42. The method according to claim 39 , wherein the first and the second content areas display content of different first and second content categories, respectively, and wherein: if the indication is of dropping the first element into the second content area, the third content items are of the second content category of the second content area, and if the indication is of dropping the second element into the first content area, the fourth content items are of the first content category of the first content area. 43. The method according to claim 42 , wherein the method further comprises, before receiving the indication of dragging and dropping of the first element or the second element, causing, by the server system, the web browser to display (a) in the first and the second content areas, the respective first and second content items requested from respective one or more online content sources, and (b) respective names of the online content sources in association with the respective first and second content areas.