I also found this series of tutorials helpful
Idratherbewriting
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I find active examples to look at helpful when reading documentation.
simple tutorial from swagger
Swaggerhub
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The response validation pointers in this link are very helpful.
Swagger
OAS 3 This page applies to OpenAPI 3 - the latest version of the OpenAPI Specification. If you use OpenAPI 2 (fka Swagger), visit OpenAPI 2 pages. You can use the enum keyword to specify possible values of a request parameter or a model property.