code: func Copy(src, dst fs.Filesystem, from, to string) (err error) {
  	return withPreparedTarget(dst, from, to, func() error {
  		return copyFileContents(src, dst, from, to)
  	})
  }
docs: // Copy copies the file content from source to destination.
  // Tries hard to succeed on various systems by temporarily tweaking directory
  // permissions and removing the destination file when necessary.