Adding a table element to DocBook 4.3

Hello -

I'm new to Docbook, and am trying to add an element for a borderless
table <tableBorderless>.  I've created the following customization
layer, and it seems to work correctly.  However, before proceeding
further, I'm hoping one of you can tell me whether I did this correctly?
(I'm a bit nervous about whether what I'm doing will break something
else).  Thanks!


<!ENTITY  % local.formal.class "|tableBorderless">
<!ENTITY % DocBookDTD  PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
                       "http://docbook.org/xml/4.3/docbookx.dtd">
%DocBookDTD;

<!ELEMENT tableBorderless %ho; (%tbl.table.mdl;)>

<!ATTLIST tableBorderless
     frame           CDATA   #FIXED "none"
       colsep         CDATA   #FIXED "0"
        rowsep        CDATA  #FIXED "0"
        %tbl.table.att;
        %bodyatt;
        %secur;
>