Export a file package.

Info.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>

<key>CFBundleDocumentTypes</key>
<array>
  <dict>
    <key>CFBundleTypeIconSystemGenerated</key>
    <integer>0</integer>
    <key>CFBundleTypeName</key>
    <string>My Demo Bundle File</string>
    <key>CFBundleTypeRole</key>
    <string>Editor</string>
    <key>LSHandlerRank</key>
    <string>Default</string>
    <key>LSItemContentTypes</key>
    <array>
      <string>sb.lao.dev.demo</string>
    </array>
    <key>LSTypeIsPackage</key>
    <true/>
    <key>NSUbiquitousDocumentUserActivityType</key>
    <string>$(PRODUCT_BUNDLE_IDENTIFIER).demo</string>
  </dict>
</array>

<key>UTExportedTypeDeclarations</key>
<array>
  <dict>
    <key>UTTypeConformsTo</key>
    <array>
      <string>public.data</string>
      <string>public.content</string>
      <string>com.apple.package</string>
    </array>
    <key>UTTypeIcons</key>
    <dict/>
    <key>UTTypeIdentifier</key>
    <string>sb.lao.dev.demo</string>
    <key>UTTypeTagSpecification</key>
    <dict>
      <key>public.filename-extension</key>
      <array>
        <string>mydemo</string>
      </array>
    </dict>
  </dict>
</array>

</dict>
</plist>