How to set per-filetype tab size?

VS Code configures language specific settings in settings.json

• Shortcut is: Command Palette (⇧⌘P) then: Preferences: Configure Language Specific Settings

Example of setting.json changing tabsize

{
    "[sass]": {
        "editor.tabSize": 2
    },
    "[html]": {
        "editor.tabSize": 4
    },
    "[javascript]": {
        "editor.tabSize": 2
    }
}

These are not nested inside any other object, they are defined at the root.