validation of json-ld to context schema

Hi,

I found the schema.org context (by using the ACCEPT header and curl). However, what was returned confused me. I expected the context to layout the type/class hierarchy of the vocabulary but instead it provided a limited number of key names definitions.

When I use Google Email Markup Tester it does validate the keys are allowed for a given type, but I don't see how the context at schema.org provides the information that a type of Person exists. Hence my question is how is this validation done with schema.org? Not asking how goggle does it, but how does the spec direct the look up that a Person is a type?

Thank you,

Robert