gnome-shell/data/osk-layouts/digits.json

{
  "levels": [
    {
      "level": "",
      "mode": "default",
      "rows": [
        [
          {
            "strings": [
              "7"
            ]
          },
          {
            "strings": [
              "8"
            ]
          },
          {
            "strings": [
              "9"
            ]
          },
          {
            "action": "delete",
            "iconName": "edit-clear-symbolic"
          }
        ],
        [
          {
            "strings": [
              "4"
            ]
          },
          {
            "strings": [
              "5"
            ]
          },
          {
            "strings": [
              "6"
            ]
          },
          {
            "iconName": "keyboard-enter-symbolic",
            "keyval": "0xff0d",
            "height": 2
          }
        ],
        [
          {
            "strings": [
              "1"
            ]
          },
          {
            "strings": [
              "2"
            ]
          },
          {
            "strings": [
              "3"
            ]
          }
        ],
        [
          {
            "width": 3,
            "strings": [
              "0"
            ]
          },
          {
            "action": "hide",
            "iconName": "keyboard-hide-symbolic"
          }
        ]
      ]
    }
  ],
  "name": "Digits"
}