code: func (p *printer) open(format string, a ...interface{}) func() {
  	p.Printf(format, a...)
  	p.Printf(" {\n")
  	p.Out.Level++
  	return func() {
  		p.Out.Level--
  		p.Printf("}\n")
  	}
  }
docs: // open prints a string, followed by " {\n" and increases indentation level.
  // Returns a function that decreases indentation level and closes the brace.
  // Usage: defer open("package x")()