diff --git a/tests/utils/test_substitution.py b/tests/utils/test_substitution.py
index 66cb501..60a49aa 100644
--- a/tests/utils/test_substitution.py
+++ b/tests/utils/test_substitution.py
@@ -5,7 +5,7 @@
 
 from varst.utils.rst_file import RstFile
 from varst.utils.substitution import Substitution
-from varst.utils.substitution import substitution_text
+from varst.utils.substitution import substitution_def
 
 TEST_DATA_PATH = os.path.join(
     Path(__file__).resolve().parent.parent, 'data',
@@ -29,5 +29,15 @@ def test_find_substitution(substitution: Substitution):
         substitution.find("not exist name")
 
 
+def test_update_substitution(substitution: Substitution):
+    substitution.update("status", "true")
+    substitution.update("with whitespace", "true")
+
+    assert substitution.find("status") == """.. |status| replace:: true\n"""
+    assert substitution.find(
+        "with whitespace",
+    ) == """.. |with whitespace| replace:: true\n"""
+
+
 def test_create_substitution():
-    assert substitution_text("key", "value") == """.. |key| replace:: value"""
+    assert substitution_def("key", "value") == """.. |key| replace:: value"""
diff --git a/varst/utils/parser.py b/varst/utils/parser.py
index 8d7fdec..7933d73 100644
--- a/varst/utils/parser.py
+++ b/varst/utils/parser.py
@@ -20,8 +20,8 @@ def __init__(self) -> None:
         self.sub_pairs: Dict[str, str] = {}
 
         self._parser.add_argument(
-            "name=value", nargs="*",
-            help="name-value pairs of substitutions",
+            "substitutions", nargs="*",
+            help="pairs of substitution definition. format is 'text=data'",
             type=_pattern_type,
         )
         self._parser.add_argument(
@@ -52,7 +52,7 @@ def parse(self, argv: Optional[Sequence[str]]) -> None:
         self.input_file = self.output_file = arg_dict['input']
         if arg_dict['output'] is not None:
             self.output_file = arg_dict['output']
-        self.sub_pairs = _parse_kv(arg_dict['name=value'])
+        self.sub_pairs = _parse_kv(arg_dict['substitutions'])
 
 
 _VARIABLE_PATTERN = re.compile(r"[^=]+=[^=]+")
diff --git a/varst/utils/substitution.py b/varst/utils/substitution.py
index 30b7d95..64afdea 100644
--- a/varst/utils/substitution.py
+++ b/varst/utils/substitution.py
@@ -8,48 +8,48 @@ class Substitution:
     def __init__(self, rst_file: RstFile):
         self.rst_file = rst_file
 
-    def find(self, name: str) -> str:
-        """Find substitution text by name.
+    def find(self, text: str) -> str:
+        """Find substitution definition by substitution text.
 
         Args:
-            name: The string value of substitution name.
+            text: The string value of substitution text.
         Returns:
-            Returns substitution text if substitution exists.
+            Returns substitution definition if it exists.
         Raises:
-            KeyError: If substitution is not in file.
+            KeyError: If substitution definition is not in file.
 
         """
-        pattern = fr"""\.\.[ ]+\|({name})\|"""
+        pattern = fr"""\.\.[ ]+\|({text})\|"""
 
         for content in self.rst_file.contents:
             if re.match(pattern, content):
                 return content
-        raise KeyError(name)
+        raise KeyError(text)
 
-    def update(self, name: str, value: str) -> None:
-        """Update substitution text with name to value.
+    def update(self, text: str, data: str) -> None:
+        """Update substitution definition by using substitution text and data.
 
         Args:
-            name: The string value of substitution name.
-            value: The string value of substitution text.
+            text: The string value of substitution text.
+            data: The string value of substitution data.
 
         """
-        origin = self.find(name)
-        new = substitution_text(name, value)
+        origin = self.find(text)
+        new = substitution_def(text, data)
 
         origin_idx = self.rst_file.contents.index(origin)
         self.rst_file.contents.pop(origin_idx)
         self.rst_file.contents.insert(origin_idx, new + "\n")
 
 
-def substitution_text(name: str, value: str) -> str:
-    """Create substitution text by using name and value.
+def substitution_def(text: str, data: str) -> str:
+    """Create substitution definition by using substitution text and data.
 
     Args:
-        name: The string value of substitution name.
-        value: The string value of substitution text.
+        text: The string value of substitution text.
+        data: The string value of substitution data.
     Returns:
-        Returns substitution text.
+        Returns substitution definition.
 
     """
-    return f'.. |{name}| replace:: {value}'
+    return f'.. |{text}| replace:: {data}'