Atomic REs:
  c	matches the character c (for non-metacharacters c)
  "^"	matches the empty string at the beginning of a line
    "$"	matches the empty string at the end of a line
  "."	matches any single character (except \000 and \n)

Escape sequences:
    "\b"	matches backspace
    "\f"	matches formfeed
    "\n"	matches newline (linefeed)
    "\r"	matches carriage return
    "\t"	matches tab
    "\"ddd	matches the character with octal code ddd.
    "\"c	matches the character c (e.g., \\ for \, \" for ")
  "\x"dd  matches the character with hex code dd.

Character classes:
    [...]	matches any character in "..."
    [^...]	a complemented character list, which matches any character not
     in the list "..."

Compound regular expressions, where A and B are REs:
    A|B	matches A or B
    AB	matches A followed by B
    A?	matches zero or one As
    A*	matches zero or more As
    A+	matches one or more As
    A{n}	matches n copies of A
    A{n,}	matches n or more copies of A
    A{n,m}	matches from n to m copies of A
    (A)	matches A