Passes attribute information up to the parent TableTag.
When we hit the end of the tag, we simply let our parent (which better be a TableTag) know what the user wants to do with this column. We do that by simple registering this tag with the parent. This tag's only job is to hold the configuration information to describe this particular column. The TableTag does all the work.
@return int
@throws JspException if this tag is being used outside of a <display:list...> tag.
@see javax.servlet.jsp.tagext.Tag#doEndTag()