code: function signIn (selection) {
    return dom.create('div').class('sign-in')
      .add(dom.create('input').class('username-input'))
      .add(dom.create('input').class('password-input'))
      .add(dom.create('button').class('sign-in-button').text('Sign in'))
  }
docs: creates a sign in block for the @signIn entity