// A self-contained demonstration of the problem follows...
this._register('vscode.diff', (left: URI, right: URI, label: string) => {
    return this._commands.executeCommand('_workbench.diff', left, right, label);
}, {
    description: 'Opens the provided resources in the diff editor to compare their contents.',
    args: [
        { name: 'left', description: 'Uri of the resource for the left hand side of the diff editor', constraint: value => value instanceof URI },
        { name: 'right', description: 'Uri of the resource for the right hand side of the diff editor', constraint: value => value instanceof URI },
        { name: 'label', description: 'Label to use for the diff editor', constraint: value => typeof value === 'string' }
    ]
});