Combinability of JSON strings into a valid JSON string

Question

Is it possible guaranty that the string generated in the following way always results in a valid JSON?

I use for example the following template with the placeholder &someanotherjsonstring&

{
  "key1": "value1",
  "key2": "value2",
  "data": &someanotherjsonstring&
}

So, if someotherjsonstring is {"a": 1} the resulting string is a valid JSON string:

{
  "key1": "value1",
  "key2": "value2",
  "data": { "a":1 }
}

According to my understanding of the JSON syntax grammar [1] the resulting string will always be a valid JSON, because:

1. A valid JSON string is either array or object.
2. A value of a key:value pair can be array or object (among other data types).

Is my understanding of the JSON grammar correct and I can assume the expanded template is always a valid JSON, independently of the placeholder value, given it is a valid JSON?

References

1. https://www.json.org/json-en.html