html-nformaltable nested inside html-table in DocBook 5.0

["Frank Steimke" <f-steimke@berger-und-steimke.de>]

Hi,
i would like to use an informaltable nested inside a table in docbook 5.0.
There was a thread about this subject on this mailing list in March 2010
[1]. I do understand that there are problems with the CALS table model. So
the advice was to switch to the HTML table model: "DocBook has allowed full
nested tables since version 4.3, when HTML table markup was 
added. You can put a table inside a <td> element in DocBook's HTML table
markup. And there are no restrictions on row or column spans."

However, this fragment leads to an error:
<table>
        <caption>HTML Table</caption>
        <tbody>
            <tr>
                <td>
                    <informaltable>
                        <tbody>
                            <tr>
                                <td>1</td>
                                <td>2</td>
                            </tr>
                        </tbody>
                    </informaltable>
                </td>
            </tr>
        </tbody>
    </table>
Error message is generated from schematron: "informaltable must not occur in
the descendants of table".

It will validate, however, if I change the outer "table" to "informaltable"
and remove the caption. I can`t see any reason for this restriction in case
of HTML table model. I think that the schematron rule should check the table
model and claim an error only in case of CALS tables.

[1] https://lists.oasis-open.org/archives/docbook/201003/msg00004.html

Sincerely,
Frank