conclude treaties, issue passports, make appointments, make regulations, incorporate, and receive lands that escheat to the Crown. The third type, unwritten principles, are values that are incorporated into the Canadian constitution by the preamble of the Constitution Act, 1867. Unlike conventions, they are legally binding. In Reference re Secession of Quebec, the court ruled that there are at least four fundamental tenets that form part of the constitutional framework of Canada: federalism, democracy, constitutionalism and the rule of law, and respect for minorities. Other principles include responsible government, representation by population, judicial independence, parliamentary supremacy, and an implied bill of rights. In one case, the Provincial Judges Reference (1997), it was found a law can be held invalid for contradicting unwritten principles, in this case judicial independence. Judicial interpretations Interpretation of the Canadian Constitution has been significantly affected by the decisions of courts, which have the power to determine the meaning of phrases and, in some cases, even read into it rules that are implied but not directly stated. Canada's Constitution is not limited to the interpretation that would have been used by the original drafters, unlike countries that use originalism to interpret their constitutions. The power of the courts to update the meaning of the Constitution to fit with changing times was first established in the Persons Case, which decided that the word "person" in the Constitution included women. The Persons Case referred to this principle as the "living tree doctrine". In spite of the living tree doctrine, for several decades Canadian courts mostly limited themselves to interpreting the Constitution for issues of jurisdiction. For example, courts determined that airports were within the power of the federal government even though the original drafters of the Constitution could not have conceived of an airport. After the introduction of the Constitution Act, 1982 and the Charter of Rights and Freedoms, Canadian courts became much more active in interpretation of Constitutional questions. One notable example is in the case of gay rights and section 15(1) of the Charter. Section 15(1) lists grounds against which people may not be discriminated by the government, and includes race, religion, sex, and others, but it does not limit itself to the listed grounds. Consequently, numerous provincial superior court cases, beginning with Halpern v. Canada (Attorney General) in Ontario, ruled that sexual orientation was an unwritten protected ground under section 15(1). Repealed constitutional documents Repealed before 1982