code: function injectAndGetClassName(useImportant, styleDefinitions) {
      // Filter out falsy values from the input, to allow for
      // `css(a, test && c)`
      var validDefinitions = styleDefinitions.filter(function (def) {
          return def;
      });
  
      // Break if there aren't any valid styles.
      if (validDefinitions.length === 0) {
          return "";
      }
  
      var className = validDefinitions.map(function (s) {
          return s._name;
      }).join("-o_O-");
      injectStyleOnce(className, '.' + className, validDefinitions.map(function (d) {
          return d._definition;
      }), useImportant);
  
      return className;
  }
docs: Inject styles associated with the passed style definition objects, and return
  an associated CSS class name.
  
  @param {boolean} useImportant If true, will append !important to generated
  CSS output. e.g. {color: red} -> "color: red !important".
  @param {Object[]} styleDefinitions style definition objects as returned as
  properties of the return value of StyleSheet.create().