In V 2.7, the markers mean [A,B), right?
What are the keyboard commands to set the markers for lossless cutting ("copy" mode)?
A marker use up/down arrow keys?
B marker use up/down arrow keys PLUS ONE RIGHT ARROW? ")" means it will copy until the frame BEFORE the one that you see on the screen when you set the "B" marker?
No, when saving, the frame matching the marker B is included into the resulting video. When deleting, the frame at B is excluded from deletion unless B is at or beyond the last frame of the video. I refer to the latest git master, some bugs in 2.7.0 and earlier versions, now fixed, resulted in last frames not fitting into the total duration and thus dropped (first at the demuxer level, then in muxer gate code).
The standard keyboard shortcuts to set markers are Ctrl+PgUp and Ctrl+PgDown, but I prefer enabling alternative shortcuts (freely configurable, with "I" and "O" as default values for setting markers A and B).
Use keyframe based navigation to set marker A (PgUp/PgDown). The same is preferable for B as well, but depending on video also non-intra frames can be used for that.