code: protected String getId(FaceletContext ctx)
      {
          if (this.id != null)
          {
              return this.id.getValue(ctx);
          }
          return ctx.generateUniqueId(this.tagId);
      }
docs: If the id TagAttribute was specified, get it's value, otherwise generate a unique id from our tagId.
  
  @see TagAttribute#getValue(FaceletContext)
  @param ctx
  FaceletContext to use
  @return what should be a unique Id