非限制性定语从句标志词在英语语法中用于描述主句内容，包括"which"用于描述属性或特点，"who"用于描述人的身份或特点，"whom"作为宾语修饰先行词，以及"where"用于描述地点或场所。这些标志词可以帮助更好地理解和运用非限制性定语从句。
which
which 是非限制性定语从句中最常用的标志词之一。通常用于修饰先行词，进一步描述它的属性或特点。例如：
- My favorite color is blue, which is the color of the ocean.
- The book, which I read last night, was very interesting.
who
who 通常用来修饰人，表示这个人的身份或特点。例如：
- My friend, who is a doctor, gave me some medical advice.
- The teacher, who is very strict, never allows us to use our phones in class.
whom
whom 通常用来作宾语，修饰先行词。例如：
- I met my neighbor, whom I haven't seen in a long time.
- The person, whom I was looking for, finally arrived.
where
where 通常用来描述地点或场所，修饰先行词。例如：
- I visited New York City, where I saw the Statue of Liberty.
- The museum, where I went last weekend, had a lot of interesting exhibits.
