code: function (data) {
      var schema = this.schema;
      if (typeof data === 'string') { return data; }
      if (this.isSingleProperty) { return stringifyProperty(data, schema); }
      data = stringifyProperties(data, schema);
      return styleParser.stringify(data);
    }
docs: Stringify properties if necessary.
  
  Only called from `Entity.setAttribute` for properties whose parsers accept a non-string
  value (e.g., selector, vec3 property types).
  
  @param {object} data - Complete component data.
  @returns {string}