### More Explanation of Param() 

- [param_type] OpenAPI 3.0 distinguishes between the following parameter types based on the parameter location: 
**header, path, query, cookie**. [more](https://swagger.io/docs/specification/describing-parameters/)

- [name] parameter name. If param_type is :path, it must correspond to the associated path segment form 
the routing path, for example: the path is `/good/:id`, then you have to declare a path parameter with name `id`.

- [type] parameter (schema) type. Support all [data types](https://github.com/OAI/OpenAPI-Specification/blob/OpenAPI.next/versions/3.0.0.md#dataTypes) defined in OAS.   
In addition, you can use `format` in schema_hash to define in fine detail the data type being used, like: 
int32, float, date ...  
All the types you can use are:
  - **String, 'binary', 'base64'**
  - **Integer, Long, 'int32', 'int64', Float, Double**
  - **File** (it will be converted as `{ type: 'string', format: OpenApi.config.dft_file_format }`)
  - **Date, DateTime**
  - **Boolean**
  - **Array**: `Array[String]` or `[String]`
  - Nested Array: `[[[Integer]]]`
  - **Object**: you can use just `Object`, or use a hash to declare its properties `{ id!: Integer, name: String }` 
  (`!` bang key means it is required).
  - Nested Object: `{ id!: Integer, name: { first: String, last: String } }`
  - Nested Array and Object: `[[{ id!: Integer, name: { first: String, last: String } }]]`
  - **:ComponentKey**: the Symbol value pass to type will generate a Schema Reference Object link 
  to the component correspond to ComponentKey.
  
  You can use `Object.const_set()` to define a constant that does not exist, but note that 
  the value you set could not be a Symbol (it will be explained as a Ref Object), should be a String.

- [required] :opt or :req

- The [[schema]](https://github.com/OAI/OpenAPI-Specification/blob/OpenAPI.next/versions/3.0.0.md#schemaObject) defining the type used for the parameter. 
schema_hash(optional) will be used to generate Schema Object inside Parameter Object.  
[source code](https://github.com/zhandao/zero-rails_openapi/blob/master/lib/oas_objs/schema_obj.rb)  
You can set the schema by following keys (all are optional), the words in parentheses are available aliases of the keys:  
  - enum (values, allowable_values)  
  Must be Array or Range(will be converted to Array)
  - value (must_be, allowable_value)  
  Single value, could be a String, Array ...  
  - range (number_range)  
  Allow value in this continuous range. Set this field like this: `{ gt: 0, le: 5 }`
  - length (lth)  
  Must be an Integer, Integer Array, Integer Range, or the following format Symbol: `:gt_`, `:ge_`, `:lt_`, `:le_`, examples: :ge_5 means "greater than or equal 5"; :lt_9 means "lower than 9".
  - format (fmt)
  - is (is_a)  
    1. It's not in OAS, just an addition field for better express.You can see it as `format`, but in fact they are quite different.  
    2. Look at this example: the `format` is set to "int32", but you also want to express that this 
    schema is an "id" format —— this cannot be expressed in the current OAS version.  
    3. So I suggest that the value of `format` should related to data type, `is` should be an entity.  
    4. ZRO defaults to identify whether `is` patterns matched the name, then automatically generate `is`. 
    for example the parameter name "user_email" will generate "is: email". Default `is` options are:  
    [email phone password uuid uri url time date], to overwrite it you can set it in initializer `c.is_options = %w[]`.
    5. If type is Object, for describing each property's schema, the only way is use ref type, like: `{ id: :Id, name: :Name }`
  - pattern (regexp, pr, reg)
  - default (dft, default_value)