diff --git a/lib/hyperscript/parser.sx b/lib/hyperscript/parser.sx
index 176174be..be58d2b6 100644
--- a/lib/hyperscript/parser.sx
+++ b/lib/hyperscript/parser.sx
@@ -1164,7 +1164,9 @@
                   (let
                     ((tgt (parse-expr)))
                     (list (quote add-value) value tgt))
-                  nil))))))
+                  (error
+                    (str
+                      "Invalid 'add' syntax: expected a class (.foo), attribute, or expression with 'to'"))))))))
       (define
         parse-remove-cmd
         (fn
@@ -2973,7 +2975,7 @@
                 (let
                   ((of-filter (when (and (= event-name "mutation") (match-kw "of")) (cond ((and (= (tp-type) "ident") (or (= (tp-val) "attributes") (= (tp-val) "childList") (= (tp-val) "characterData"))) (let ((nm (tp-val))) (do (adv!) (dict "type" nm)))) ((= (tp-type) "attr") (let ((attrs (list (tp-val)))) (do (adv!) (define collect-or! (fn () (when (match-kw "or") (cond ((= (tp-type) "attr") (do (set! attrs (append attrs (list (tp-val)))) (adv!) (collect-or!))) (true (set! p (- p 1))))))) (collect-or!) (dict "type" "attrs" "attrs" attrs)))) (true nil)))))
                   (let
-                    ((event-vars (if (= (tp-type) "paren-open") (do (adv!) (define ev-coll (fn () (cond ((or (= (tp-type) "paren-close") (= (tp-type) "eof")) (do (when (= (tp-type) "paren-close") (adv!)) (list))) ((or (= (tp-type) "ident") (= (tp-type) "keyword")) (let ((nm (tp-val))) (adv!) (cons nm (ev-coll)))) (true (do (adv!) (ev-coll)))))) (ev-coll)) (list))))
+                    ((event-vars (if (= (tp-type) "paren-open") (let ((saved-p p)) (do (adv!) (if (= (tp-type) "keyword") (do (set! p saved-p) (list)) (do (define ev-coll (fn () (cond ((or (= (tp-type) "paren-close") (= (tp-type) "eof")) (do (when (= (tp-type) "paren-close") (adv!)) (list))) ((or (= (tp-type) "ident") (= (tp-type) "keyword")) (let ((nm (tp-val))) (adv!) (cons nm (ev-coll)))) (true (do (adv!) (ev-coll)))))) (ev-coll))))) (list))))
                     (let
                       ((flt (if (= (tp-type) "bracket-open") (do (adv!) (let ((f (parse-expr))) (if (= (tp-type) "bracket-close") (adv!) nil) f)) nil)))
                       (let
diff --git a/lib/hyperscript/tokenizer.sx b/lib/hyperscript/tokenizer.sx
index a62849eb..367a178d 100644
--- a/lib/hyperscript/tokenizer.sx
+++ b/lib/hyperscript/tokenizer.sx
@@ -459,7 +459,7 @@
           (define
             build-name
             (fn
-              (acc)
+              (acc depth)
               (cond
                 ((and (< pos src-len) (= (hs-cur) "\\") (< (+ pos 1) src-len))
                   (do
@@ -467,15 +467,35 @@
                     (let
                       ((c (hs-cur)))
                       (hs-advance! 1)
-                      (build-name (str acc c)))))
-                ((and (< pos src-len) (or (hs-ident-char? (hs-cur)) (= (hs-cur) ":") (= (hs-cur) "[") (= (hs-cur) "]") (= (hs-cur) "(") (= (hs-cur) ")") (= (hs-cur) "&")))
+                      (build-name (str acc c) depth))))
+                ((and (< pos src-len) (= (hs-cur) "["))
                   (do
                     (let
                       ((c (hs-cur)))
                       (hs-advance! 1)
-                      (build-name (str acc c)))))
+                      (build-name (str acc c) (+ depth 1)))))
+                ((and (< pos src-len) (= (hs-cur) "]"))
+                  (do
+                    (let
+                      ((c (hs-cur)))
+                      (hs-advance! 1)
+                      (build-name
+                        (str acc c)
+                        (if (> depth 0) (- depth 1) 0)))))
+                ((and (< pos src-len) (> depth 0) (or (= (hs-cur) "(") (= (hs-cur) ")")))
+                  (do
+                    (let
+                      ((c (hs-cur)))
+                      (hs-advance! 1)
+                      (build-name (str acc c) depth))))
+                ((and (< pos src-len) (or (hs-ident-char? (hs-cur)) (= (hs-cur) ":") (= (hs-cur) "&")))
+                  (do
+                    (let
+                      ((c (hs-cur)))
+                      (hs-advance! 1)
+                      (build-name (str acc c) depth))))
                 (true acc))))
-          (build-name "")))
+          (build-name "" 0)))
       (define
         hs-emit!
         (fn
diff --git a/shared/static/wasm/sx/hs-parser.sx b/shared/static/wasm/sx/hs-parser.sx
index 176174be..be58d2b6 100644
--- a/shared/static/wasm/sx/hs-parser.sx
+++ b/shared/static/wasm/sx/hs-parser.sx
@@ -1164,7 +1164,9 @@
                   (let
                     ((tgt (parse-expr)))
                     (list (quote add-value) value tgt))
-                  nil))))))
+                  (error
+                    (str
+                      "Invalid 'add' syntax: expected a class (.foo), attribute, or expression with 'to'"))))))))
       (define
         parse-remove-cmd
         (fn
@@ -2973,7 +2975,7 @@
                 (let
                   ((of-filter (when (and (= event-name "mutation") (match-kw "of")) (cond ((and (= (tp-type) "ident") (or (= (tp-val) "attributes") (= (tp-val) "childList") (= (tp-val) "characterData"))) (let ((nm (tp-val))) (do (adv!) (dict "type" nm)))) ((= (tp-type) "attr") (let ((attrs (list (tp-val)))) (do (adv!) (define collect-or! (fn () (when (match-kw "or") (cond ((= (tp-type) "attr") (do (set! attrs (append attrs (list (tp-val)))) (adv!) (collect-or!))) (true (set! p (- p 1))))))) (collect-or!) (dict "type" "attrs" "attrs" attrs)))) (true nil)))))
                   (let
-                    ((event-vars (if (= (tp-type) "paren-open") (do (adv!) (define ev-coll (fn () (cond ((or (= (tp-type) "paren-close") (= (tp-type) "eof")) (do (when (= (tp-type) "paren-close") (adv!)) (list))) ((or (= (tp-type) "ident") (= (tp-type) "keyword")) (let ((nm (tp-val))) (adv!) (cons nm (ev-coll)))) (true (do (adv!) (ev-coll)))))) (ev-coll)) (list))))
+                    ((event-vars (if (= (tp-type) "paren-open") (let ((saved-p p)) (do (adv!) (if (= (tp-type) "keyword") (do (set! p saved-p) (list)) (do (define ev-coll (fn () (cond ((or (= (tp-type) "paren-close") (= (tp-type) "eof")) (do (when (= (tp-type) "paren-close") (adv!)) (list))) ((or (= (tp-type) "ident") (= (tp-type) "keyword")) (let ((nm (tp-val))) (adv!) (cons nm (ev-coll)))) (true (do (adv!) (ev-coll)))))) (ev-coll))))) (list))))
                     (let
                       ((flt (if (= (tp-type) "bracket-open") (do (adv!) (let ((f (parse-expr))) (if (= (tp-type) "bracket-close") (adv!) nil) f)) nil)))
                       (let
diff --git a/shared/static/wasm/sx/hs-tokenizer.sx b/shared/static/wasm/sx/hs-tokenizer.sx
index a62849eb..367a178d 100644
--- a/shared/static/wasm/sx/hs-tokenizer.sx
+++ b/shared/static/wasm/sx/hs-tokenizer.sx
@@ -459,7 +459,7 @@
           (define
             build-name
             (fn
-              (acc)
+              (acc depth)
               (cond
                 ((and (< pos src-len) (= (hs-cur) "\\") (< (+ pos 1) src-len))
                   (do
@@ -467,15 +467,35 @@
                     (let
                       ((c (hs-cur)))
                       (hs-advance! 1)
-                      (build-name (str acc c)))))
-                ((and (< pos src-len) (or (hs-ident-char? (hs-cur)) (= (hs-cur) ":") (= (hs-cur) "[") (= (hs-cur) "]") (= (hs-cur) "(") (= (hs-cur) ")") (= (hs-cur) "&")))
+                      (build-name (str acc c) depth))))
+                ((and (< pos src-len) (= (hs-cur) "["))
                   (do
                     (let
                       ((c (hs-cur)))
                       (hs-advance! 1)
-                      (build-name (str acc c)))))
+                      (build-name (str acc c) (+ depth 1)))))
+                ((and (< pos src-len) (= (hs-cur) "]"))
+                  (do
+                    (let
+                      ((c (hs-cur)))
+                      (hs-advance! 1)
+                      (build-name
+                        (str acc c)
+                        (if (> depth 0) (- depth 1) 0)))))
+                ((and (< pos src-len) (> depth 0) (or (= (hs-cur) "(") (= (hs-cur) ")")))
+                  (do
+                    (let
+                      ((c (hs-cur)))
+                      (hs-advance! 1)
+                      (build-name (str acc c) depth))))
+                ((and (< pos src-len) (or (hs-ident-char? (hs-cur)) (= (hs-cur) ":") (= (hs-cur) "&")))
+                  (do
+                    (let
+                      ((c (hs-cur)))
+                      (hs-advance! 1)
+                      (build-name (str acc c) depth))))
                 (true acc))))
-          (build-name "")))
+          (build-name "" 0)))
       (define
         hs-emit!
         (fn