The VoiceOver modifier is a key or set of keys you press with one or more other keys to enter VoiceOver commands. You can set the VoiceOver modifier to be the Caps Lock key or the Control and Option keys pressed at the same time.
VoiceOver commands are represented as VO-key, where VO represents the VoiceOver modifier specified in the General category of VoiceOver Utility. For example, the VoiceOver command VO-Shift-M means to press the VoiceOver modifier along with the Shift and M keys at the same time. Depending on the VoiceOver modifier you’re using, you press Caps Lock-Shift-M or Control-Option-Shift-M.
When the VoiceOver modifier is locked, you don’t have to press it, making it easier to enter VoiceOver commands. For example, to enter VO-Shift-M you would press just the Shift and M keys at the same time. To lock the VoiceOver modifier, press VO-; (press it again to unlock the modifier).
To be able to use the Caps Lock key for typing uppercase letters when the VoiceOver modifier is set to Caps Lock, quickly press the Caps Lock key twice.