App-def ext elems and MustUnderstand

[MURATA Makoto]

Dear colleagues,

I still do not understand app-def ext elems.  MS Excel 2007
happily accepts the following workbook.xml in my workbook.
In this example, an application-defined extension element
(ext) contains an element in the
"http://schemas.openxmlformats.org/spreadsheetml/2006/main"
namespace, which is obviously understood.  Thus, the MCE
processor should scan this element, encounter
@MustUnderstand within the element and report
an error.

But no errors are reported.  When does the MCE processor
skip the content of app defined ext elems?

Regards,
Makoto

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"
    xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships">
    <fileVersion appName="xl" lastEdited="4" lowestEdited="5" rupBuild="4507"/>
    <workbookPr showInkAnnotation="0" autoCompressPictures="0"/>
    <bookViews>
        <workbookView xWindow="3480" yWindow="705" windowWidth="19365"
windowHeight="12120"
            tabRatio="500"/>
    </bookViews>
    <sheets>
        <sheet name="Sheet1" sheetId="1" r:id="rId1"/>
    </sheets>
    <calcPr calcId="125725"/>
    <extLst xmlns:mce="http://schemas.openxmlformats.org/markup-compatibility/2006">
        <ext uri="{7523E5D3-25F3-A5E0-1632-64F254C22452}"
xmlns:mx="http://www.example.com" xmlns:bar="http://www.example1.com">
            <mx:ArchID Flags="2"/>
            <mx:ArchID Flags="2"/>
            <mx:ArchID Flags="2"/>
            <sheets>
                <sheet name="Sheet1" sheetId="1" r:id="rId2"
mce:MustUnderstand="mx bar"/>
            </sheets>
        </ext>
        <ext uri="{7523E5D3-25F3-A5E0-1632-64F254C22452}"
xmlns:mx="http://www.example.com">
            <mx:ArchID Flags="2"/>
        </ext>
    </extLst>
</workbook>

-- 

Praying for the victims of the Japan Tohoku earthquake

Makoto