types/src/main/java/com/google/common/html/types/SafeHtmlBuilder.java
public SafeHtmlBuilder appendContent(Iterable<SafeHtml> htmls) {
    checkNotVoidElement();
    for (SafeHtml html : htmls) {
      contents.add(html);
    }
    return this;
  }
public SafeHtmlBuilder appendContent(Iterable<SafeHtml> htmls) {
    checkNotVoidElement();
    for (SafeHtml html : htmls) {
      contents.add(html);
    }
    return this;
  }
Appends the given {@code htmls} as this element's content, in the sequence the Iterable returns
them.

@throws IllegalStateException if this builder represents a void element