OpenXML: Support for strict mode documents

[Chase Tingley]

From https://groups.google.com/forum/#!topic/okapi-devel/dlzVxf-rjRc

Recently we got some XLSX documents that could not be handled by the OpenXML filter. We found out that those documents use another namespace for their elements. > Take a look at the ".rels" part of the file:

<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"> 
        <Relationship Id="rId3" Type="http://purl.oclc.org/ooxml/officeDocument/relationships/extendedProperties" Target="docProps/app.xml"/> 
        <Relationship Id="rId2" Type="http://schemas.openxmlformats.org/package/2006/relationships/metadata/core-properties" Target="docProps/core.xml"/> 
        <Relationship Id="rId1" Type="http://purl.oclc.org/ooxml/officeDocument/relationships/officeDocument" Target="xl/workbook.xml"/> 
</Relationships> 

After some googling I found out that "purl.oclc.org" indicates the "ISO/IEC 29500 Strict". "schemas.openxmlformats.org" is used by "ISO/IEC 29500 Transitional". You can find some more information here: https://en.wikipedia.org/wiki/Office_Open_XML