Rich snippet is a short note of the content on the website to help the user to choose the correct result they are looking after..
Schema is the library Structure data is the skeletal structure of information and Rich snippet is the end result of both schema and structure data..
It gives the skeletal structure to the website content makes it easy for the crawlers to understand the website content..
If you want to add special strategic to markup for your website you can use the markup generator to modify content to your need..
Based on the crawler's level of understanding about your website based on the snippets you provide the snippet shown will vary.
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