it just means it accepts modelines with the "doublescan" flag.
and if you add a modeline, say 400x300 @ 55Hz to the "usermodes.txt" it will show up in windows as 55hz, if you add the same modeline to custom15khz.txt it will show up as 60hz.
1) I am not sure I understand. Can you explain further. Do I still need add:
remove 288x240
remove 296x240
remove 256x256
remove 240x240
remove 321x256
remove 352x256
remove 352x264
modeline '288x240@59,305' 6,2 288 320 352 396 240 243 246 264 -hsync -vsync
modeline '296x240@59,305' 6,2 296 320 352 396 240 243 246 264 -hsync -vsync
modeline '352x256@59,697' 7,47 352 352 405 450 256 257 260 271 -hsync -vsync
modeline '352x264@59,697' 7,47 352 352 405 458 264 265 268 279 -hsync -vsync
modeline '321x256@59,014' 6,45 321 336 368 414 256 258 261 280 -hsync -vsync
modeline '256x256@60,436' 5,3 256 272 296 352 256 260 263 277 -hsync -vsync
modeline '240x240@60,436' 5,3 240 240 280 336 240 244 247 261 -hsync -vsync
or is that incorperated into the new version of soft 15.
2) Concering usermodes.txt do they conflict with the standard modelines? What i mean is can you have the same resolution twice with a different refresh? How does one tell Mame to use the different refresh? Is it just for example 240x240@59 in the rom.ini file for the game?