src/main/java/org/jsoup/nodes/Element.java
/**
     Set the element's {@code class} attribute to the supplied class names.
     @param classNames set of classes
     @return this element, for chaining
     */
Set the element's  class attribute to the supplied class names.
Set the element ' s class attribute to the supplied class names .
public Element classNames(Set<String> classNames) {
        Validate.notNull(classNames);
        attributes.put("class", StringUtils.join(classNames, " "));
        return this;
    }
public Element classNames ( Set < String > classNames ) { Validate . notNull ( classNames ) ; attributes . put ( "class" , StringUtils . join ( classNames , " " ) ) ; return this ; }
Set the element's {@code class} attribute to the supplied class names.
Set the element ' s { @code class } attribute to the supplied class names .