code: def ReverseCloseExpression(clean_lines, linenum, pos):
    
    line = clean_lines.elided[linenum]
    if line[pos] not in ')}]>':
      return (line, 0, -1)
  
    # Check last line
    (start_pos, stack) = FindStartOfExpressionInLine(line, pos, [])
    if start_pos > -1:
      return (line, linenum, start_pos)
  
    # Continue scanning backward
    while stack and linenum > 0:
      linenum -= 1
      line = clean_lines.elided[linenum]
      (start_pos, stack) = FindStartOfExpressionInLine(line, len(line) - 1, stack)
      if start_pos > -1:
        return (line, linenum, start_pos)
  
    # Did not find start of expression before beginning of file, give up
    return (line, 0, -1)
docs: If input points to ) or } or ] or >, finds the position that opens it.
  
    If lines[linenum][pos] points to a ')' or '}' or ']' or '>', finds the
    linenum/pos that correspond to the opening of the expression.
  
    Args:
      clean_lines: A CleansedLines instance containing the file.
      linenum: The number of the line to check.
      pos: A position on the line.
  
    Returns:
      A tuple (line, linenum, pos) pointer *at* the opening brace, or
      (line, 0, -1) if we never find the matching opening brace.  Note
      we ignore strings and comments when matching; and the line we
      return is the 'cleansed' line at linenum.