InvariantTextEntity, unexpected properties fixes

js/entity/InvariantTextEntity.js

@@ -0,0 +1,16 @@
+// @ts-check
+
+import IEntity from "./IEntity"
+
+export default class InvariantTextEntity extends IEntity {
+
+    static lookbehind = "INVTEXT"
+    static attributes = {
+        value: String,
+    }
+
+    constructor(options = {}) {
+        super(options)
+        /** @type {String} */ this.value
+    }
+}