gistfile1.txt

properties: {
  title: {
    type: 'string',
    maxLength: 140,
    
    conditional: {
      optional: true,
      when: function () {         // The 'optional' attribute only takes effect if this function returns true
        return !this.published;   // So the title is only optional if the article hasn't been published.
      }
    }
  }
}