function flattenChildren(children) {
	  var content = '';

	  // Flatten children and warn if they aren't strings or numbers;
	  // invalid types are ignored.
	  React.Children.forEach(children, function (child) {
	    if (child == null) {
	      return;
	    }
	    if (typeof child === 'string' || typeof child === 'number') {
	      content += child;
	    } else if (!didWarnInvalidOptionChildren) {
	      didWarnInvalidOptionChildren = true;
	      process.env.NODE_ENV !== 'production' ? warning(false, 'Only strings and numbers are supported as <option> children.') : void 0;
	    }
	  });

	  return content;
	}
Implements an <option> host component that warns when `selected` is set.