add True, False, None

src/grammar.json

@@ -122,6 +122,14 @@
         {
           "type": "SYMBOL",
           "name": "translated_string"
+        },
+        {
+          "type": "SYMBOL",
+          "name": "boolean"
+        },
+        {
+          "type": "SYMBOL",
+          "name": "none"
         }
       ]
     },
@@ -150,6 +158,23 @@
         }
       ]
     },
+    "boolean": {
+      "type": "CHOICE",
+      "members": [
+        {
+          "type": "STRING",
+          "value": "True"
+        },
+        {
+          "type": "STRING",
+          "value": "False"
+        }
+      ]
+    },
+    "none": {
+      "type": "STRING",
+      "value": "None"
+    },
     "attribute": {
       "type": "PATTERN",
       "value": "[a-zA-Z0-9][a-zA-Z0-9_]*(?:\\.[a-zA-Z0-9][a-zA-Z0-9_]*)*"