in source/ext/extref.py [0:0]
def _class(self):
class_text = "reference {0}".format(self._url_type())
if self._type() == 'image':
class_text += " image-reference preview"
if self._type() == 'logo':
class_text += " image-reference logo"
if self._custom_class() is not None:
class_text += " {0}".format(self._custom_class())
return class_text