From: Ralf Brown aill >
# .docx, .pptx, and .xlsx are XML plus other files inside a ZIP
# archive. The first member file is normally "[Content_Types].xml".
# but some libreoffice generated files put this later. Perhaps skip
# the "[Content_Types].xml" test?
# Since MSOOXML doesn't have anything like the uncompressed "mimetype"
# file of ePub or OpenDocument, we'll have to scan for a filename
# which can distinguish between the three types
EFTA00502754