ISO/IEC 29500 defines two conformance classes for Office Open XML. Files nearly always use Transitional. A Strict file has the same parts and elements in a different set of namespaces.
Namespaces
| What | Transitional | Strict |
|---|---|---|
| PresentationML | http://schemas.openxmlformats.org/presentationml/2006/main | http://purl.oclc.org/ooxml/presentationml/main |
| DrawingML | http://schemas.openxmlformats.org/drawingml/2006/main | http://purl.oclc.org/ooxml/drawingml/main |
| Relationships | http://schemas.openxmlformats.org/officeDocument/2006/relationships | http://purl.oclc.org/ooxml/officeDocument/relationships |
The explorer treats the two the same way once the namespaces are matched, and shows which form a file uses.