DEFINE_STRING_CB(source_citation, sub_cit_page_start, page)
DEFINE_STRING_CB(source_citation, sub_cit_even_start, event)
DEFINE_STRING_CB(source_citation, sub_cit_even_role_start, role)
DEFINE_STRING_CB(source_citation, sub_cit_page_start, page)
DEFINE_STRING_CB(source_citation, sub_cit_even_start, event)
DEFINE_STRING_CB(source_citation, sub_cit_even_role_start, role)