code: public static <B extends TextBoxBase> B setPlaceholderText (B box, String placeholder)
      {
          return _formSupport.setPlaceholderText(box, placeholder);
      }
docs: Set the placeholder text to use on the specified form field.
  This text will be shown when the field is blank and unfocused.
  
  Note: To safely read the text from this TextBox on all browsers, use
  getText(TextBoxBase, placeholder). This is because on legacy browsers that don't support
  HTML5 form awesomeness, the text will actually be set in the field when it is unfocused.