code: public List<String> getAttr(String content, String selector, String attributeKey) {
  
  		Element body = parseContent(content);
  		
  		List<Element> elements = body.select(selector);
  		List<String> attrs = new ArrayList<String>();
  		
  		for (Element element : elements) {
  			String attrValue = element.attr(attributeKey);
  			attrs.add(attrValue);
  		}
  		
  		return attrs;
  	}
docs: Retrieves attribute value on elements in HTML. Will return all attribute values for the
  selector, since there can be more than one element.
  
  @param content
  HTML content to read attributes from
  @param selector
  CSS selector for elements to find
  @param attributeKey
  Attribute name
  @return Attribute values for all matching elements. If no elements are found, empty list is
  returned.
  @since 1.0