import re

re.compile(r"(?<!a|b)");
re.compile(r"(?<!<error descr="Alternation alternatives need to have the same length inside lookbehind">a|bc</error>)");
re.compile(r"(?<!a{3}})");
re.compile(r"(?<!a<weak_warning descr="Fixed repetition range">{3,3}</weak_warning>})");
re.compile(r"(?<!a<error descr="Unequal min and max in counted quantifier not allowed inside lookbehind">{3,4}</error>})");
re.compile(r"(?<!a|b<weak_warning descr="Single repetition">{1}</weak_warning>)")
re.compile(r"(?<!abcd|(ab){2})")
re.compile(r"(?<!abcde|x(ab){2})")
re.compile(r"(?<!a(ab|cd)|xyz)")