ParEdit (paredit.el) is a minor mode for performing structured editing of S-expression data. The typical example of this would be Lisp or Scheme source code.

ParEdit helps keep parentheses balanced and adds many keys for moving S-expressions and moving around in S-expressions. Its behavior can be jarring for those who may want transient periods of unbalanced parentheses, such as when typing parentheses directly or commenting out code line by line.