GNOME 3 Lockscreen Keyboard

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I need an onscreen keyboard to use with my tablet on the GNOME 3 lockscreen. The GNOME docs say that I can use any onscreen keyboard that supports XEmbed, though I have no idea if either of the two included keyboards (eekboard, and whatever the keyboard included with the accessibility options is) support this. Once I have a keyboard that supports it, GNOME docs say to:

set /apps/gnome-screensaver/embeddedkeyboardenable=TRUE

set /apps/gnome-screensaver/embeddedkeyboardcommand="name-of-keyboard-binary --xid"

But I need a keyboard first. All the examples on the internet are either using 'onboard', Ubuntu's default OSK or 'matchbox-keyboard' which doesn't appear to exist anymore. Please help!