you need to look in sdl_mapper.cpp

(for example there are some blocks for the numeric keyboard that are different on linux)

Thank you. I see that I have to modify:

1#if defined (MACOSX)
2		/* nothing */

so that it includes something like:

1	sdlkey_map[0x68]=SDLK_INSERT;

But I'm still baffled at figuring out what to use in place of 0x68 to indicate MOD3-Down.

A keycode utility in OS X tells me that the key code is 125 / 0x7d, and the modifier (Cmd) is 11534600 /0xb00108.

I'll be very grateful if any OS X expert can tell me what to do next.

I'm not sure I'm getting any closer to an answer but I see that

sdlkey_map[0x7d] is the Down key

sdlkey_map[0x37] is the left Cmd key

and somehow I've got to make these two combine to be

SDLK_INSERT;

But if I simply try something like this, I get an error (which will probably be obvious to everyone here):

sdlkey_map[0x7d]+sdlkey_map[0x37]=SDLK_INSERT;

Is this getting anywhere, or should I just give up trying?