diff --git a/src/jolt/clojure/string.clj b/src/jolt/clojure/string.clj
index 807813e..7cda7dc 100644
--- a/src/jolt/clojure/string.clj
+++ b/src/jolt/clojure/string.clj
@@ -51,10 +51,16 @@
   (str-reverse-b s))
 
 (defn split
-  ([s re]
-   (vec (str-split re s)))
+  ([s re] (split s re 0))
   ([s re limit]
-   (vec (take limit (str-split re s)))))
+   ;; Java Pattern.split semantics: limit > 0 caps the parts (trailing empties
+   ;; kept); limit < 0 splits fully and keeps trailing empties; limit 0 (the
+   ;; default) splits fully then drops trailing empty strings — but a no-match
+   ;; result ([input], the only 1-element case) is returned as-is.
+   (let [parts (vec (str-split re s (if (pos? limit) limit nil)))]
+     (if (and (zero? limit) (> (count parts) 1))
+       (loop [v parts] (if (and (seq v) (= "" (peek v))) (recur (pop v)) v))
+       parts))))
 
 (defn split-lines
   "Split s on \\n or \\r\\n, returning a vector of lines."
diff --git a/src/jolt/core_coll.janet b/src/jolt/core_coll.janet
index 20804e4..a841daa 100644
--- a/src/jolt/core_coll.janet
+++ b/src/jolt/core_coll.janet
@@ -418,7 +418,7 @@
       (array? coll) (make-vec coll)
       (tuple? coll) (make-vec coll)
       (struct? coll) (make-vec (map |(in (kvs coll) (+ (* $ 2) 1)) (range (/ (length (kvs coll)) 2))))
-      (string? coll) (make-vec (map |(string/from-bytes $) (string/bytes coll)))
+      (string? coll) (make-vec (map make-char (string/bytes coll)))
       (make-vec @[]))))
 
 # Bulk-build a map value from a native array of [k v] pairs, mirroring
diff --git a/src/jolt/core_extra.janet b/src/jolt/core_extra.janet
index d8220d5..a6c0ab5 100644
--- a/src/jolt/core_extra.janet
+++ b/src/jolt/core_extra.janet
@@ -247,10 +247,16 @@
 # (core/20-coll.clj) — pure over get on the tagged value the constructor builds.
 
 # String split/replace that accept either a literal string or a regex value.
-(defn core-str-split [pat s]
+(defn core-str-split [pat s &opt limit]
   (if (regex? pat)
-    (re-split pat s)
-    (string/split pat s)))
+    (re-split pat s limit)
+    (let [parts (string/split pat s)]
+      # literal separator: a positive limit caps the part count; rejoin the tail
+      # with the (constant) separator to recover the unsplit remainder.
+      (if (and limit (> limit 0) (> (length parts) limit))
+        (array/push (array/slice parts 0 (- limit 1))
+                    (string/join (array/slice parts (- limit 1)) pat))
+        parts))))
 (defn core-str-replace-all [pat repl s]
   (if (regex? pat)
     (re-replace-all pat s repl)
diff --git a/src/jolt/core_types.janet b/src/jolt/core_types.janet
index f65590c..ca35f03 100644
--- a/src/jolt/core_types.janet
+++ b/src/jolt/core_types.janet
@@ -167,6 +167,9 @@
     (phm? c) (phm-entries c)
     # sorted colls iterate their comparator-ordered entries/elements
     (core-sorted? c) (sorted-entries-arr c)
+    # a string is a seqable of CHARS in Clojure (not bytes/1-char strings) — mirror
+    # core-seq so vec/set/into over a string agree with seq (jolt-dl4s)
+    (string? c) (tuple ;(map make-char (string/bytes c)))
     # byte array (Janet buffer) -> array of byte values
     (buffer? c) (let [a @[]] (each x c (array/push a x)) a)
     # struct map literal (no :jolt/type marker — not a symbol/char) -> entries
diff --git a/src/jolt/interop/java_base.janet b/src/jolt/interop/java_base.janet
index 20fe1bb..5488545 100644
--- a/src/jolt/interop/java_base.janet
+++ b/src/jolt/interop/java_base.janet
@@ -82,7 +82,9 @@
                       "file.separator" "/"
                       "user.dir" (os/cwd)
                       "user.home" (or (os/getenv "HOME") "")
-                      "java.io.tmpdir" (or (os/getenv "TMPDIR") "/tmp")})})
+                      "java.io.tmpdir" (or (os/getenv "TMPDIR") "/tmp")})
+   # terminate the process with the given status code
+   "exit" (fn [&opt status] (os/exit (if (nil? status) 0 status)))})
 
 # sentinels portable code compares against. jolt numbers are doubles, so these
 # are the f64 approximations.
diff --git a/src/jolt/regex.janet b/src/jolt/regex.janet
index 4b239d0..d0e12cf 100644
--- a/src/jolt/regex.janet
+++ b/src/jolt/regex.janet
@@ -8,8 +8,10 @@
 # Supported: literals, `.`, char classes `[...]`/`[^...]` (ranges, POSIX,
 # `\d \w \s` etc.), quantifiers `* + ? {n} {n,} {n,m}` (greedy + lazy `?`),
 # groups `(...)` (numbered), non-capturing `(?:...)`, lookahead `(?=...)`/`(?!...)`,
-# alternation `|`, anchors `^ $ \b \B`, escapes, inline flag `(?i)`.
-# Not supported: lookbehind, backreferences, named groups (rare; documented).
+# alternation `|`, anchors `^ $ \b \B`, escapes, inline flag `(?i)`, and
+# single-digit backreferences `\1`..`\9` (a backreferenced group matches
+# possessively — no backtracking back into it; rare in practice).
+# Not supported: lookbehind, named groups (rare; documented).
 
 (defn- chr [s] (get s 0))
 (defn regex? [x] (and (table? x) (= :jolt/regex (x :jolt/type))))
@@ -189,6 +191,10 @@
             p {:op :pred :peg p}
             (= nc (chr "b")) {:op :anchor :kind :wordb}
             (= nc (chr "B")) {:op :anchor :kind :nwordb}
+            # \1..\9 backreference (single digit) — record the referenced group so
+            # the emitter knows to tag-capture its text
+            (and (>= nc (chr "1")) (<= nc (chr "9")))
+              (let [n (- nc (chr "0"))] (put (st :refs) n true) {:op :backref :n n})
             {:op :char :b (esc-byte nc) :ci ci})))
     (= c (chr "^")) (do (++ (st :pos)) {:op :anchor :kind :start})
     (= c (chr "$")) (do (++ (st :pos)) {:op :anchor :kind :end})
@@ -241,9 +247,9 @@
   (if (= 1 (length branches)) (branches 0) {:op :alt :items branches})))
 
 (defn- parse [source]
-  (def st @{:s source :pos 0 :ngroup 0 :ci false :ml false :dotall false})
+  (def st @{:s source :pos 0 :ngroup 0 :ci false :ml false :dotall false :refs @{}})
   (def ast (parse-alt st))
-  [ast (st :ngroup) (st :ml)])
+  [ast (st :ngroup) (st :ml) (st :refs)])
 
 # ============================================================
 # Emit: AST -> PEG grammar (continuation passing)
@@ -256,7 +262,7 @@
     ~(set ,(string/from-bytes (lower-b b) (upper-b b)))
     ~(set ,(string/from-bytes b))))
 
-(defn- make-emitter [grammar ml]
+(defn- make-emitter [grammar ml refs]
   (var ctr 0)
   (defn fresh [] (++ ctr) (keyword (string "r" ctr)))
   (var emit nil)
@@ -292,19 +298,38 @@
                                             ~(choice ,(emit item (keyword r)) ,k)
                                             ~(choice ,k ,(emit item (keyword r)))))
                            (keyword r))
-                         (do (var acc k) (var c (- hi lo))
+                         # Each optional level is its OWN grammar rule that
+                         # references the previous level by name. Inlining instead
+                         # (choice (emit item acc) acc) duplicates `acc` per level,
+                         # so {0,n} built a structure the PEG compiler expanded to
+                         # 2^n nodes and hung (jolt-3xur). Naming keeps it O(n).
+                         (do (def kr (fresh)) (put grammar kr k)
+                             (var acc (keyword kr)) (var c (- hi lo))
                              (while (> c 0)
-                               (set acc (if greedy ~(choice ,(emit item acc) ,acc)
-                                                   ~(choice ,acc ,(emit item acc))))
+                               (let [r (fresh)]
+                                 (put grammar r (if greedy ~(choice ,(emit item acc) ,acc)
+                                                          ~(choice ,acc ,(emit item acc))))
+                                 (set acc (keyword r)))
                                (-- c))
                              acc)))
              (var acc tail) (var c lo)
              (while (> c 0) (set acc (emit item acc)) (-- c))
              acc)
       :group (let [n (ast :n)]
-               ~(sequence (/ (position) ,(fn [p] [n :s p]))
-                          ,(emit (ast :item)
-                                 ~(sequence (/ (position) ,(fn [p] [n :e p])) ,k))))
+               (if (and refs (refs n))
+                 # backreferenced group: also capture its text under tag :gN so a
+                 # later \N can (backmatch). The item runs with just the end-marker
+                 # as its continuation, so it matches POSSESSIVELY — backtracking
+                 # INTO a backreferenced group isn't supported (rare; the usual
+                 # (x)...\1 patterns don't need it).
+                 (let [tag (keyword (string "g" n))]
+                   ~(sequence (/ (position) ,(fn [p] [n :s p]))
+                              (<- ,(emit (ast :item) ~(/ (position) ,(fn [p] [n :e p]))) ,tag)
+                              ,k))
+                 ~(sequence (/ (position) ,(fn [p] [n :s p]))
+                            ,(emit (ast :item)
+                                   ~(sequence (/ (position) ,(fn [p] [n :e p])) ,k)))))
+      :backref ~(sequence (backmatch ,(keyword (string "g" (ast :n)))) ,k)
       :ncgroup (emit (ast :item) k)
       :look (if (ast :neg)
               ~(sequence (not ,(emit (ast :item) 0)) ,k)
@@ -327,9 +352,9 @@
   emit)
 
 (defn compile-regex [source]
-  (def [ast ngroups ml] (parse source))
+  (def [ast ngroups ml refs] (parse source))
   (def grammar @{})
-  (def emit (make-emitter grammar ml))
+  (def emit (make-emitter grammar ml refs))
   # group 0 = whole match: mark start, body, mark end
   (def body (emit ast ~(sequence (/ (position) ,(fn [p] [0 :e p])) 0)))
   (put grammar :main ~(sequence (/ (position) ,(fn [p] [0 :s p])) ,body))
@@ -354,8 +379,11 @@
   (def starts (array/new-filled (+ ngroups 1)))
   (def ends (array/new-filled (+ ngroups 1)))
   (each m marks
-    (let [n (m 0)]
-      (if (= (m 1) :s) (put starts n (m 2)) (put ends n (m 2)))))
+    # backreferenced groups also leave a tagged TEXT capture (a string) on the
+    # stack — skip those; only the [n :s/:e pos] position tuples carry group spans
+    (when (indexed? m)
+      (let [n (m 0)]
+        (if (= (m 1) :s) (put starts n (m 2)) (put ends n (m 2))))))
   (def groups (array/new-filled (+ ngroups 1)))
   (var n 0)
   (while (<= n ngroups)
@@ -401,10 +429,14 @@
   # `(if-let [m (re-seq ...)] ...)` works — an empty seq would be truthy.
   (if (= 0 (length out)) nil out))
 
-(defn re-split [re s]
+(defn re-split [re s &opt limit]
+  # limit (Java Pattern.split n>0): at most `limit` parts — stop after limit-1
+  # splits and keep the rest of the string as the final unsplit part. nil/<=0
+  # splits at every match.
   (def re (re-pattern re))
+  (def lim (if (and limit (> limit 0)) limit nil))
   (def out @[]) (var pos 0) (var last 0)
-  (while (<= pos (length s))
+  (while (and (<= pos (length s)) (or (nil? lim) (< (length out) (dec lim))))
     (def g (match-at re s pos))
     (if (and g (> (length (in g 0)) 0))
       (do (array/push out (string/slice s last pos))
diff --git a/test/spec/host-interop-spec.janet b/test/spec/host-interop-spec.janet
index ca7ed39..17e1b55 100644
--- a/test/spec/host-interop-spec.janet
+++ b/test/spec/host-interop-spec.janet
@@ -159,6 +159,8 @@
    "[(Boolean/parseBoolean \"true\") (Boolean/parseBoolean \"false\") (Boolean/parseBoolean \"yes\")]"]
   ["System/getenv is a map" "true"
    "(string? (get (System/getenv) \"HOME\"))"]
+  # registered, so (System/exit n) resolves; actual exit verified via subprocess
+  ["System/exit resolves" "true" "(fn? System/exit)"]
   # NOT every? alone — it held vacuously while seq over a raw host table
   # yielded nothing, hiding that read-system-env came back empty
   ["getenv entries destructure (non-empty)" "true"
diff --git a/test/spec/regex-spec.janet b/test/spec/regex-spec.janet
index 264a2ef..78de377 100644
--- a/test/spec/regex-spec.janet
+++ b/test/spec/regex-spec.janet
@@ -62,3 +62,22 @@
   [".matches partial -> false" "false" "(.matches \"abcd\" \"a.c\")"]
   [".replaceAll regex"   "\"a-b-c\"" "(.replaceAll \"a_b_c\" \"_\" \"-\")"]
   [".replaceFirst regex" "\"a-b_c\"" "(.replaceFirst \"a_b_c\" \"_\" \"-\")"])
+
+(defspec "regex / bounded quantifiers (jolt-3xur)"
+  ["exact {n}"        "\"aaa\""  "(re-matches #\"a{3}\" \"aaa\")"]
+  ["range {n,m} max"  "\"aaaa\"" "(re-find #\"a{2,4}\" \"aaaaa\")"]
+  ["zero lower {0,n}" "\"aa\""   "(re-find #\"a{0,3}\" \"aa\")"]
+  ["{n,} unbounded"   "\"aaaa\"" "(re-find #\"a{2,}\" \"aaaa\")"]
+  # nested bounded quantifiers must not blow up the PEG compiler — this used to
+  # expand to ~2^61 nodes and hang at compile time.
+  ["nested bounds compile" "true"
+   "(boolean (re-matches #\"[a-z](?:[a-z]{0,61}[a-z])?(?:-[a-z]{0,61}[a-z])*\" \"abc-def\"))"])
+
+(defspec "regex / backreferences (jolt-xtss)"
+  ["repeated char"      "true"   "(boolean (re-find #\"(.)\\1\" \"abba\"))"]
+  ["no repeat = nil"    "nil"    "(re-find #\"(.)\\1\" \"abc\")"]
+  ["thematic-break run" "true"   "(boolean (re-matches #\"([-*_])\\1\\1\" \"---\"))"]
+  ["mismatched run"     "nil"    "(re-matches #\"([-*_])\\1\\1\" \"-*_\")"]
+  ["repeated word"      "[\"the the\" \"the\"]" "(re-find #\"(\\w+) \\1\" \"say the the word\")"]
+  ["group still captures" "[\"x=x\" \"x\"]" "(re-matches #\"(\\w+)=\\1\" \"x=x\")"]
+  ["html tag pair"      "true"   "(boolean (re-matches #\"<(\\w+)>.*</\\1>\" \"<b>hi</b>\"))"])
diff --git a/test/spec/strings-spec.janet b/test/spec/strings-spec.janet
index daeceeb..731734c 100644
--- a/test/spec/strings-spec.janet
+++ b/test/spec/strings-spec.janet
@@ -20,6 +20,22 @@
   ["pr-str of a defn"   "\"#'user/gg\"" "(pr-str (defn gg [x] x))"]
   ["seq of string"      "[\\a \\b]"  "(seq \"ab\")"])
 
+(defspec "string as a seqable of chars (jolt-dl4s)"
+  ["vec of string"       "[\\a \\b]" "(vec \"ab\")"]
+  ["into [] of string"   "[\\a \\b]" "(into [] \"ab\")"]
+  ["set of string"       "true"      "(= #{\\a \\b} (set \"ab\"))"]
+  ["into #{} of string"  "true"      "(= #{\\a \\b} (into #{} \"ab\"))"]
+  ["set dedups chars"    "2"         "(count (set \"aab\"))"]
+  ["mapv over string"    "[\\a \\b]" "(mapv identity \"ab\")"])
+
+(defspec "clojure.string / split limit (jolt-ik3a)"
+  ["neg keeps trailing"  "[\"a\" \"\" \"\"]" "(do (require (quote [clojure.string :as s])) (s/split \"a,,\" #\",\" -1))"]
+  ["zero trims trailing" "[\"a\"]"           "(do (require (quote [clojure.string :as s])) (s/split \"a,,\" #\",\" 0))"]
+  ["omitted trims"       "[\"a\"]"           "(do (require (quote [clojure.string :as s])) (s/split \"a,,\" #\",\"))"]
+  ["positive caps parts" "[\"a\" \"b,c\"]"   "(do (require (quote [clojure.string :as s])) (s/split \"a,b,c\" #\",\" 2))"]
+  ["empty string"        "[\"\"]"            "(do (require (quote [clojure.string :as s])) (s/split \"\" #\",\"))"]
+  ["interior empties kept" "[\"a\" \"\" \"b\"]" "(do (require (quote [clojure.string :as s])) (s/split \"a,,b\" #\",\"))"])
+
 (defspec "clojure.string"
   ["join"               "\"a,b,c\""  "(do (require (quote [clojure.string :as s])) (s/join \",\" [\"a\" \"b\" \"c\"]))"]
   ["join no sep"        "\"abc\""    "(do (require (quote [clojure.string :as s])) (s/join [\"a\" \"b\" \"c\"]))"]