code: func (d *Directive) possibleParserDirective(line string) error {
  	if d.processingComplete {
  		return nil
  	}
  
  	tecMatch := tokenEscapeCommand.FindStringSubmatch(strings.ToLower(line))
  	if len(tecMatch) != 0 {
  		for i, n := range tokenEscapeCommand.SubexpNames() {
  			if n == "escapechar" {
  				if d.escapeSeen {
  					return errors.New("only one escape parser directive can be used")
  				}
  				d.escapeSeen = true
  				return d.setEscapeToken(tecMatch[i])
  			}
  		}
  	}
  
  	d.processingComplete = true
  	return nil
  }
docs: // possibleParserDirective looks for parser directives, eg '# escapeToken=<char>'.
  // Parser directives must precede any builder instruction or other comments,
  // and cannot be repeated.