code: def FlagCxx14Features(filename, clean_lines, linenum, error):
    
    line = clean_lines.elided[linenum]
  
    include = Match(r'\s*#\s*include\s+[<"]([^<"]+)[">]', line)
  
    # Flag unapproved C++14 headers.
    if include and include.group(1) in ('scoped_allocator', 'shared_mutex'):
      error(filename, linenum, 'build/c++14', 5,
            ('<%s> is an unapproved C++14 header.') % include.group(1))
docs: Flag those C++14 features that we restrict.
  
    Args:
      filename: The name of the current file.
      clean_lines: A CleansedLines instance containing the file.
      linenum: The number of the line to check.
      error: The function to call with any errors found.