code: public SafeHtmlBuilder setPoster(SafeUrl value) {
      if (!POSTER_SAFE_URL_ELEMENT_WHITELIST.contains(elementName)) {
        throw new IllegalArgumentException(
            "Attribute \"poster\" with a SafeUrl value can only be used "
                + "by one of the following elements: "
                + POSTER_SAFE_URL_ELEMENT_WHITELIST);
      }
      return setAttribute("poster", value.getSafeUrlString());
    }
docs: Sets the {@code poster} attribute for this element.
  
  <p>The attribute {@code poster} with a {@code SafeUrl} value is allowed on these elements:
  
  <ul>
  <li>{@code video}
  </ul>
  
  @throws IllegalArgumentException if the {@code poster} attribute with a {@code SafeUrl} value
  is not allowed on this element