Statutory interpretation is the process by which courts interpret and apply legislation. Some amount of interpretation is often necessary when a case involves a statute. Sometimes the words of a statute have a plain and a straightforward meaning. But in many cases, there is some ambiguity in the words of the statute that must be resolved by the judge. To find the meanings of statutes, judges use various tools and methods of statutory interpretation, including traditional canons of statutory interpretation, legislative history, and purpose. In common law jurisdictions, the judiciary may apply rules of statutory interpretation both to legislation enacted by the legislature and to delegated legislation such as administrative agency regulations. History Statutory interpretation first became significant in common law systems, of which historically England is the exemplar. In Roman and civil law, a statute (or code) guides the magistrate, but there is no judicial precedent. In England, Parliament historically failed to enact a comprehensive code of legislation, which is why it was left to the courts to develop the common law; and having decided a case and given reasons for the decision, the decision would become binding on later courts. Accordingly, a particular interpretation of a statute would also become binding, and it became necessary to introduce a consistent framework for statutory interpretation. In the construction (interpretation) of statutes, the principle aim of the court must be to carry out the "intention of Parliament", and the English courts developed three main rules (plus some minor ones) to assist them in the task. These were: the mischief rule, the literal rule, and the golden rule. Statutes may be presumed to incorporate certain components, as Parliament is "presumed" to have intended their inclusion. For example: Offences defined in criminal statutes are presumed to require mens rea (a guilty intention by the accused): Sweet v Parsley. A statute is presumed to make no changes in the common law. A statute is presumed not to remove an individual's liberty, vested rights, or property. A statute is presumed not to apply to the Crown. A statute is presumed not to empower a person to commit a criminal offence. A statute is presumed not to apply retrospectively (whereas the common law is "declaratory": Shaw v DPP). A statute is to be interpreted so as to uphold international treaties to which the UK is a party. In the case of EU law, any statutory provision