A citator can also be used to determine whether a statute or regulation has been amended, repealed, superseded, or held unconstitutional.
This is important for legal systems in which the binding authority of a case is contingent on precedent.
Citators often include annotations indicating the history and treatment of a case in citing opinions.
Shepard's notes 'history' as affirmed, modified, reversed, same case, Superseded, or vacated; and 'treatment' as criticised, distinguished, explained, j dissenting opinion, ~ consenting opinion, Limited, overruled, or questioned.
[2] Frank Shepard Company started publishing citators in New York City in 1873 and other companies provided similar services at around the same time, e.g. George Fred Williams's Massachusetts citations: a table of cases, overruled, denied, doubted, criticised, approved, and cited by the Supreme Judicial Court (Boston, 1878).