def file_manifest(self, location):
        """
        An iterator through the files in a location which yields item elements
        suitable for insertion into the package manifest.
        """
        #Maps file extensions to mimetypes
        mimetypes = {'.jpg': 'image/jpeg',
                     '.jpeg': 'image/jpeg',
                     '.xml': 'application/xhtml+xml',
                     '.png': 'image/png',
                     '.css': 'text/css',
                     '.ncx': 'application/x-dtbncx+xml',
                     '.gif': 'image/gif',
                     '.tif': 'image/tif',
                     '.pdf': 'application/pdf',
                     '.xhtml': 'application/xhtml+xml',
                     '.ttf': 'application/vnd.ms-opentype',
                     '.otf': 'application/vnd.ms-opentype'}

        current_dir = os.getcwd()
        os.chdir(location)
        for dirpath, _dirnames, filenames in os.walk('.'):
            dirpath = dirpath[2:]  # A means to avoid dirpath prefix of './'
            for fn in filenames:
                fn_ext = os.path.splitext(fn)[-1]
                item = etree.Element('item')
                #Here we set three attributes: href, media-type, and id
                if not dirpath:
                    item.attrib['href'] = fn
                else:
                    item.attrib['href'] = '/'.join([dirpath, fn])
                item.attrib['media-type'] = mimetypes[fn_ext]
                #Special handling for common image types
                if fn_ext in ['.jpg', '.png', '.tif', '.jpeg']:
                    #the following lines assume we are using the convention
                    #where the article doi is prefixed by 'images-'
                    item.attrib['id'] = '-'.join([dirpath[7:],
                                                  fn.replace('.', '-')])
                else:
                    item.attrib['id'] = fn.replace('.', '-')
                yield item
        os.chdir(current_dir)
An iterator through the files in a location which yields item elements
        suitable for insertion into the package manifest.