/usr/share/X11/xkb/compat/accessx is in xkb-data 2.16-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52  | default partial xkb_compatibility "basic" {
    interpret AccessX_Enable {
	action= LockControls(controls=AccessXKeys);
    };
};
partial xkb_compatibility "full" {
    interpret AccessX_Enable {
	action= LockControls(controls=AccessXKeys);
    };
    interpret AccessX_Feedback_Enable {
	action= LockControls(controls=AccessXFeedback);
    };
    interpret RepeatKeys_Enable {
	action= LockControls(controls=RepeatKeys);
    };
    interpret SlowKeys_Enable {
	action= LockControls(controls=SlowKeys);
    };
    interpret BounceKeys_Enable {
	action= LockControls(controls=BounceKeys);
    };
    interpret StickyKeys_Enable {
	action= LockControls(controls=StickyKeys);
    };
    interpret MouseKeys_Enable {
	action= LockControls(controls=MouseKeys);
    };
    interpret MouseKeys_Accel_Enable {
	action= LockControls(controls=MouseKeysAccel);
    };
    interpret Overlay1_Enable {
	action= LockControls(controls=Overlay1);
    };
    interpret Overlay2_Enable {
	action= LockControls(controls=Overlay2);
    };
    interpret AudibleBell_Enable {
	action= LockControls(controls=AudibleBell);
    };
};
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