 
 ! "a(?<=b)" <regexp> "caba" over first-match
 
-
 ! capture group 1: "aaaa"  2: ""
 ! "aaaa" "(a*)(a*)" <regexp> match*
 ! "aaaa" "(a*)(a+)" <regexp> match*

[ "a" ] [ "ab" "a(?=b)(?=b)" <regexp> first-match >string ] unit-test
[ "a" ] [ "ba" "a(?<=b)(?<=b)" <regexp> first-match >string ] unit-test
[ "a" ] [ "cab" "a(?=b)(?<=c)" <regexp> first-match >string ] unit-test

! [ "{Lower}" <regexp> ] [ invalid-range? ] must-fail-with


! [ t ] [ "fxxbar" "(?!foo).{3}bar" <regexp> matches? ] unit-test
! [ f ] [ "foobar" "(?!foo).{3}bar" <regexp> matches? ] unit-test

! [ f ] [ "foobxr" "foo\\z" <regexp> match-head ] unit-test
! [ 3 ] [ "foo" "foo\\z" <regexp> match-head ] unit-test

