I have been following the document OfficeXMLMarkupExplained_en.docx, and I tried to create the Hello World docx file. I have created the individual XML files, renamed _rels/.rels.xml to _rels/.rels, and used the OS X zip command to create the docx file. When I try to open this file in Word (Mac) 2011, I get the message:
The Open XML file HelloWorld.docx cannot be opened because there are problems with the contents or the file name might contain invalid characters (for example, \/).
I suspect this is because the internal file names include _rels/.rels, rather than _rels\.rels. Tell this ain't true.
It ain't true. The problem was a missing "+" in the document type of one of the files.