diff --git a/beautiful-racket-lib/br/indent.rkt b/beautiful-racket-lib/br/indent.rkt
index 518cd2d..7f6ae29 100644
--- a/beautiful-racket-lib/br/indent.rkt
+++ b/beautiful-racket-lib/br/indent.rkt
@@ -1,5 +1,5 @@
 #lang racket/base
-(require racket/class)
+(require racket/class racket/gui/base racket/list)
 (provide (all-defined-out))
 
 (module+ test
@@ -10,7 +10,7 @@
 (define indent-width 2)
 
 (define (char text pos)
-  (send text get-character pos))
+  (and pos (send text get-character pos)))
 
 (module+ test
   (check-equal? (char t 0) #\f)
@@ -29,6 +29,19 @@
   (check-equal? (line t 10) 2)
   (check-equal? (line t 11) 2))
 
+(define (line-chars text line)
+  (and
+   (valid-line? text line)
+   (for/list ([pos (in-range (line-start text line) (add1 (line-end text line)))])
+             (char text pos))))
+
+(module+ test
+  (check-equal? (line-chars t 0) '(#\f #\o #\o #\newline))
+  (check-equal? (line-chars t 1) '(#\space #\a #\r #\newline))
+  (check-equal? (line-chars t 2) '(#\space #\space #\m #\nul))
+  (check-equal? (line-chars t 3) #f))
+
+
 (define (previous-line text pos)
   (define this-line (line text pos))
   (and (this-line . > . 0) (sub1 this-line)))
@@ -126,4 +139,25 @@
   (check-equal? (count-char t #\f) 1)
   (check-equal? (count-char t #\o) 2)
   (check-equal? (count-char t #\o 0 1) 1)
-  (check-equal? (count-char t #\newline) 2))
\ No newline at end of file
+  (check-equal? (count-char t #\newline) 2))
+
+
+(define (str->text str)
+  (define t (new text%))
+  (send t insert-port (open-input-string str))
+  t)
+
+(define (map-indenter indenter t)
+  (for/list ([line-idx (in-range (add1 (send t last-line)))])
+            (indenter t (line-start t line-idx))))
+
+(define (test-indenter indenter t-or-str)
+  (define t (if (string? t-or-str) (str->text t-or-str) t-or-str))
+  (list->string
+   (append*
+    (for/list ([line-idx (in-range (add1 (send t last-line)))]
+               [indent (in-list (map-indenter indenter t))])
+              ;; simulate DrR indentation
+              ;; by dropping leading spaces and applying new indent.
+              (append (make-list (or indent 0) #\space)
+                      (dropf (line-chars t line-idx) (λ(x) (x . char=? . #\space))))))))
\ No newline at end of file
diff --git a/beautiful-racket/br/demo/jsonic/indenter.rkt b/beautiful-racket/br/demo/jsonic/indenter.rkt
index 4a045b1..daa56d0 100644
--- a/beautiful-racket/br/demo/jsonic/indenter.rkt
+++ b/beautiful-racket/br/demo/jsonic/indenter.rkt
@@ -1,9 +1,9 @@
-#lang br
-(require br/indent)
+#lang at-exp br
+(require br/indent sugar/debug)
 (provide indenter)
 (define indent-width 2)
 
-(define (indenter text this-pos)
+(define (indenter text [this-pos 0])
   ;; if line begins with }:
   ;; outdent to the matching {
   ;; indent to match the previous line
@@ -14,7 +14,7 @@
        (count-char text #\} 0 this-line-end)))
   (and (positive? open-braces)
        (* indent-width
-          (if ((char text (line-start text this-line)) . char=? . #\{)
+          (if ((char text (line-start-visible text this-line)) . char=? . #\{)
               (sub1 open-braces)
               open-braces))))
 
@@ -27,4 +27,24 @@
     [((char text (line-start text prev-line)) . char=? . #\{)
      (+ (or prev-indent 0) indent-width)]
     [else prev-indent]))
-|#
\ No newline at end of file
+|#
+
+(module+ test
+  (require rackunit)
+  (define test-str @string-append|{
+#lang br/demo/jsonic
+{
+"string": @$(string-append "foo" "bar")$@,
+{
+"array": @$(range 5)$@,
+"object": @$(hash "k1" "valstring" (format "~a" 42) (hash "k1" (range 10) "k2" 42))$@
+}
+// "bar" :
+}}|)
+  (displayln test-str)
+  (define indented-str (test-indenter indenter test-str))
+  (displayln indented-str)
+  (define indented-str2 (test-indenter indenter indented-str))
+  (displayln indented-str2)
+  (define indented-str3 (test-indenter indenter indented-str2))
+  (displayln indented-str3))
\ No newline at end of file