Examine source code of YouTube Remote+

{
  "manifest_version": 2,
  "name": "Youtube Remote+ for Helix and Stomp",
  "version": "1.0",
  "description": "For use with the Line6 Helix and HX Stomp. Adds shortcuts for play/pause, loop, speed, and seek to YouTube, for use with the QWERTY hotkeys feature in Helix and HX Stomp.",
  "commands": {
    "setA": {
      "suggested_key": {
        "default": "MacCtrl+Alt+1"
      },
      "description": "Set marker A"
    },
    "setB": {
      "suggested_key": {
        "default": "MacCtrl+Alt+2"
      },
      "description": "Set marker B"
    },
    "setMarker": {
      "suggested_key": {
        "default": "MacCtrl+Alt+M"
      },
      "description": "Toggle loop mark (A if nothing is set, B if A is set)"
    },
    "togglePlayPause": {
      "suggested_key": {
        "default": "MacCtrl+Alt+P"
      },
      "description": "Toggle Play/Pause"
    },
    "clearLoop": {
      "suggested_key": {
        "default": "MacCtrl+Alt+C"
      },
      "description": "Clear loop markers"
    },
    "speedUp": {
      "suggested_key": {
        "default": "MacCtrl+Alt+Up"
      },
      "description": "Speed up"
    },
    "speedDown": {
      "suggested_key": {
        "default": "MacCtrl+Alt+Down"
      },
      "description": "Speed down"
    },
    "resetSpeed": {
      "suggested_key": {
        "default": "MacCtrl+Alt+R"
      },
      "description": "Reset speed to default"
    },
    "seekFwd": {
      "suggested_key": {
        "default": "MacCtrl+Alt+Right"
      },
      "description": "Forward 10 seconds"
    },
    "seekBack": {
      "suggested_key": {
        "default": "MacCtrl+Alt+Left"
      },
      "description": "Back 10 seconds"
    },
    "toggleSeekRate": {
      "suggested_key": {
        "default": "MacCtrl+Alt+S"
      },
      "description": "Toggles seek rate between 5, 10, and 15 seconds"
    }
  },
  "background": {
    "scripts": [
      "./dist/background-bundle.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "./dist/content-bundle.js"
      ]
    }
  ],
  "permissions": [
    "storage"
  ]
}