code: @Nonnull
    public TypeaheadDataset setHeader (@Nullable final String sHeaderHTML)
    {
      return setHeader (StringHelper.hasText (sHeaderHTML) ? JSExpr.lit (sHeaderHTML) : (IJSExpression) null);
    }
docs: The header rendered before suggestions in the dropdown menu. Can be either
  a DOM element or HTML.
  
  @param sHeaderHTML
  The header to use. May be <code>null</code> or empty.
  @return this