xml - Is there a way to extend a DTD used for validation? -

i wondering whether there standard way extend dtd or whether way validate document add necessary extensions in xml file.

i have system of plugins organized packages in linux installation (i.e. plugins can depend on 1 or more plugins, loops not allowed):

             +----------------------+          +-->|  editor              |<--+          |   +----------------------+   |          |                              | +-----------------+            +-----------------+ |  locale         |            | image           | +-----------------+            +-----------------+          ^                              ^          |                              |          |   +----------------------+   |          +---|  geomap              |---+              +----------------------+ 

so, have dtd in editor plugin with, example, widget tag has attribute named auto-save this:

<!element widget (value|preset|default|state)*> <!attlist widget id id #required                  type nmtoken #required                  auto-save (double | html | int8                             | date-us | no | string) "string"> 

the fact when add locale, want auto-save attribute support type such locale-date not specific us.

similarly, image plugin may want add image type , geomap plugin use geo-location.

so in end, attlist auto-save should (obviously, order not matter):

auto-save (double | html | int8 | date-us | no            | string | locale-date | image | geo-location) "string" 

even when defining multiple dtds in xml file (xmlns=... attributes in root tag), not think can that, can we?

right can add types in editor.dtd, that's wrong define locale, image, , geomap types when plugins may not available in tree...

the 1 other solution can think of use xsd, format, how go add sub-additions of attributes , tags?