In AllegroServe's htmlgen, I noticed that the <form>, <img>, <span>, and <table> tags are defined differently from all the other HTML tags. The third argument of their definition is non-null, unlike all the other tags. The comment in the source code says that the third argument is for "attribute symbols which can name this object for subst purposes". What does this mean exactly? The documentation makes no mention of "subst".
For example, the <table> tag is defined as (def-std-html :table t :name). What is so special about the name attribute of the <table> tag?