RubyZip and MS Office .docx

To create a .docx Word document, you need to zip up a number of files. If you use the rubyzip gem (as seems natural), you'd get a nasty warning:

"Microsoft Office cannot open this file because the .zip archive file
is an unsupported version."

Instead, use the command-line zip command and it works like a charm. See another post describing a similar problem.