sentence: Some programming languages have two or more standards.
sentences_before: Most languages have official 'standards' that define the rules of how to write the source code.
sentences_after: This can happen when a new standard replaces an old one. For example, the Perl 5 standard replaced Perl 4 in 1993. It can happen because two people made two standards at the same time.
concept_name: programming language
headings: Programming language Rules