24. “The tricky part was with the Yahoo Maps ... in that you can only
check to see if you're *in* a valid OSM area, *after* you've zoomed/
moved the map, not *before* ('cause you don't know where the map
is *about* to move to) ... but *after* you've zoomed/moved the map is
already loading in new tiles ... so you need to tell it 'STOP, wait, don't
load those, load these OSM ones instead' ... and in the case of Yahoo
Maps that meant using a undocumented function that blows away
the tile cache and forces a tile reload.”