diff --git a/rag/nlp/__init__.py b/rag/nlp/__init__.py
index f61019377..add454ade 100644
--- a/rag/nlp/__init__.py
+++ b/rag/nlp/__init__.py
@@ -437,16 +437,16 @@ def not_title(txt):
     return re.search(r"[,;，。；！!]", txt)
 
 def tree_merge(bull, sections, depth):
-    
+
     if not sections or bull < 0:
         return sections
     if isinstance(sections[0], type("")):
         sections = [(s, "") for s in sections]
-    
+
     # filter out position information in pdf sections
     sections = [(t, o) for t, o in sections if
                 t and len(t.split("@")[0].strip()) > 1 and not re.match(r"[0-9]+$", t.split("@")[0].strip())]
-    
+
     def get_level(bull, section):
         text, layout = section
         text = re.sub(r"\u3000", " ",   text).strip()
@@ -465,7 +465,7 @@ def tree_merge(bull, sections, depth):
         level, text = get_level(bull, section)
         if not text.strip("\n"):
             continue
-            
+
         lines.append((level, text))
         level_set.add(level)
 
@@ -608,6 +608,26 @@ def naive_merge(sections: str | list, chunk_token_num=128, delimiter="\n。；
             cks[-1] += t
             tk_nums[-1] += tnum
 
+    custom_delimiters = [m.group(1) for m in re.finditer(r"`([^`]+)`", delimiter)]
+    has_custom = bool(custom_delimiters)
+    if has_custom:
+        custom_pattern = "|".join(re.escape(t) for t in sorted(set(custom_delimiters), key=len, reverse=True))
+        cks, tk_nums = [], []
+        for sec, pos in sections:
+            split_sec = re.split(r"(%s)" % custom_pattern, sec, flags=re.DOTALL)
+            for sub_sec in split_sec:
+                if re.fullmatch(custom_pattern, sub_sec or ""):
+                    continue
+                text = "\n" + sub_sec
+                local_pos = pos
+                if num_tokens_from_string(text) < 8:
+                    local_pos = ""
+                if local_pos and text.find(local_pos) < 0:
+                    text += local_pos
+                cks.append(text)
+                tk_nums.append(num_tokens_from_string(text))
+        return cks
+
     dels = get_delimiters(delimiter)
     for sec, pos in sections:
         if num_tokens_from_string(sec) < chunk_token_num:
@@ -657,6 +677,29 @@ def naive_merge_with_images(texts, images, chunk_token_num=128, delimiter="\n。
                 result_images[-1] = concat_img(result_images[-1], image)
             tk_nums[-1] += tnum
 
+    custom_delimiters = [m.group(1) for m in re.finditer(r"`([^`]+)`", delimiter)]
+    has_custom = bool(custom_delimiters)
+    if has_custom:
+        custom_pattern = "|".join(re.escape(t) for t in sorted(set(custom_delimiters), key=len, reverse=True))
+        cks, result_images, tk_nums = [], [], []
+        for text, image in zip(texts, images):
+            text_str = text[0] if isinstance(text, tuple) else text
+            text_pos = text[1] if isinstance(text, tuple) and len(text) > 1 else ""
+            split_sec = re.split(r"(%s)" % custom_pattern, text_str)
+            for sub_sec in split_sec:
+                if re.fullmatch(custom_pattern, sub_sec or ""):
+                    continue
+                text_seg = "\n" + sub_sec
+                local_pos = text_pos
+                if num_tokens_from_string(text_seg) < 8:
+                    local_pos = ""
+                if local_pos and text_seg.find(local_pos) < 0:
+                    text_seg += local_pos
+                cks.append(text_seg)
+                result_images.append(image)
+                tk_nums.append(num_tokens_from_string(text_seg))
+        return cks, result_images
+
     dels = get_delimiters(delimiter)
     for text, image in zip(texts, images):
         # if text is tuple, unpack it
@@ -748,6 +791,23 @@ def naive_merge_docx(sections, chunk_token_num=128, delimiter="\n。；！？"):
             images[-1] = concat_img(images[-1], image)
             tk_nums[-1] += tnum
 
+    custom_delimiters = [m.group(1) for m in re.finditer(r"`([^`]+)`", delimiter)]
+    has_custom = bool(custom_delimiters)
+    if has_custom:
+        custom_pattern = "|".join(re.escape(t) for t in sorted(set(custom_delimiters), key=len, reverse=True))
+        cks, images, tk_nums = [], [], []
+        pattern = r"(%s)" % custom_pattern
+        for sec, image in sections:
+            split_sec = re.split(pattern, sec)
+            for sub_sec in split_sec:
+                if not sub_sec or re.fullmatch(custom_pattern, sub_sec):
+                    continue
+                text_seg = "\n" + sub_sec
+                cks.append(text_seg)
+                images.append(image)
+                tk_nums.append(num_tokens_from_string(text_seg))
+        return cks, images
+
     dels = get_delimiters(delimiter)
     pattern = r"(%s)" % dels
 
@@ -789,7 +849,7 @@ class Node:
         self.level = level
         self.depth = depth
         self.texts = texts or []
-        self.children = [] 
+        self.children = []
 
     def add_child(self, child_node):
         self.children.append(child_node)
@@ -835,7 +895,7 @@ class Node:
         return self
 
     def get_tree(self):
-        tree_list = []  
+        tree_list = []
         self._dfs(self, tree_list, [])
         return tree_list
 
@@ -860,7 +920,7 @@ class Node:
         # A leaf title within depth emits its title path as a chunk (header-only section)
         elif not child and (1 <= level <= self.depth):
             tree_list.append("\n".join(path_titles))
-        
+
         # Recurse into children with the updated title path
         for c in child:
-            self._dfs(c, tree_list, path_titles)
\ No newline at end of file
+            self._dfs(c, tree_list, path_titles)