Fix code snippet in in-operator documentation

files/en-us/web/javascript/reference/operators/in/index.md

@@ -36,7 +36,7 @@ prop in object
 
 The `in` operator tests if a string or symbol property is present in an object or its prototype chain. If you want to check for only _non-inherited_ properties, use {{jsxref("Object.hasOwn()")}} instead.
 
-A property may be present in an object but have value `undefined`. Therefore, `x in obj` is not the same as `obj.x !== undefined`. To make `in` return `false` after a property is added, use the [`delete`](/en-US/docs/Web/JavaScript/Reference/Operators/delete) operator instead of setting that property's value to `undefined`.
+A property may be present in an object but have value `undefined`. Therefore, `"x" in obj` is not the same as `obj.x !== undefined`. To make `in` return `false` after a property is added, use the [`delete`](/en-US/docs/Web/JavaScript/Reference/Operators/delete) operator instead of setting that property's value to `undefined`.
 
 You can also use the `in` operator to check whether a particular [private class field or method](/en-US/docs/Web/JavaScript/Reference/Classes/Private_properties) has been defined in an object. The operator returns `true` if the property is defined, and `false` otherwise. This is known as a _branded check_, because it returns `true` if and only if the object was created with that class constructor, after which you can safely access other private properties as well.