Regular Expressions

Symbol	Meaning or use
^	# Assert position at the beginning of the string.
(?:	# Group but don't capture...
ISBN	# Match the text "ISBN".
(?:-1[03])?	# Optionally match the text "-10" or "-13".
:?	# Optionally match a literal ":".
\	# Match a space character (escaped).
)?	# Repeat the group between zero and one time.
(?=	# Assert that the following can be matched here...
[-0-9\ ]{17}$	# Match 17 hyphens, digits, and spaces, then the end
|	# of the string. Or...
[-0-9X\ ]{13}$	# Match 13 hyphens, digits, Xs, and spaces, then the
|	# end of the string. Or...
[0-9X]{10}$	# Match 10 digits and Xs, then the end of the string.
)	# End the positive lookahead.
(?:	# Group but don't capture...
97[89]	# Match the text "978" or "979".
[-\ ]?	# Optionally match a hyphen or space.
)?	# Repeat the group between zero and one time.
[0-9]{1,5}	# Match a digit between one and five times.
[-\ ]?	# Optionally match a hyphen or space.
(?:	# Group but don't capture...
[0-9]+	# Match a digit between one and unlimited times.
[-\ ]?	# Optionally match a hyphen or space.
){2}	# Repeat the group exactly two times.
[0-9X]	# Match a digit or "X".
$	# Assert position at the end of the string.