@type t() :: %Xema.Schema{
  additional_items: Xema.Behaviour.t() | t() | boolean() | nil,
  additional_properties: map() | boolean() | nil,
  all_of: [t()] | nil,
  any_of: [t()] | nil,
  caster:
    function()
    | module()
    | {module(), atom()}
    | {module(), atom(), arity()}
    | list()
    | nil,
  comment: String.t() | nil,
  const: any(),
  contains: Xema.Behaviour.t() | t() | nil,
  content_encoding: String.t() | nil,
  content_media_type: String.t() | nil,
  data: map() | nil,
  default: any(),
  definitions: map() | nil,
  dependencies: list() | map() | nil,
  description: String.t() | nil,
  else: Xema.Behaviour.t() | t() | nil,
  enum: list() | nil,
  examples: [any()] | nil,
  exclusive_maximum: boolean() | number() | nil,
  exclusive_minimum: boolean() | number() | nil,
  format: atom() | nil,
  id: String.t() | nil,
  if: Xema.Behaviour.t() | t() | nil,
  items: list() | Xema.Behaviour.t() | t() | nil,
  keys: atom() | nil,
  max_items: pos_integer() | nil,
  max_length: pos_integer() | nil,
  max_properties: pos_integer() | nil,
  maximum: number() | nil,
  min_items: pos_integer() | nil,
  min_length: pos_integer() | nil,
  min_properties: pos_integer() | nil,
  minimum: number() | nil,
  module: atom() | nil,
  multiple_of: number() | nil,
  not: t() | nil,
  one_of: [t()] | nil,
  pattern: Regex.t() | nil,
  pattern_properties: map() | nil,
  properties: map() | nil,
  property_names: Xema.Behaviour.t() | t() | nil,
  ref: Xema.Ref.t() | nil,
  required: MapSet.t() | nil,
  schema: String.t() | nil,
  then: Xema.Behaviour.t() | t() | nil,
  title: String.t() | nil,
  type: type() | [type()],
  unique_items: boolean() | nil,
  validator:
    function()
    | module()
    | {module(), atom()}
    | {module(), atom(), arity()}
    | list()
    | nil
}

The struct contains the keywords for a schema.

• additional_items disallow additional items, if set to false. The keyword can also contain a schema to specify the type of additional items.
• additional_properties disallow additional properties, if set to true.
• 'all_of' a list of schemas they must all be valid.
• 'any_of' a list of schemas with any valid schema.
• caster a custom caster. This can be a function, a tuple with module and function name, or a Xema.Caster behaviour.
• comment for the schema.
• const specifies a constant.
• content_encoding annotation for the encoding.
• content_media_type annotation for the media type.
• contains validates a list whether any item is valid for the given schema.
• data none schema data.
• default this keyword can be used to supply a default value for JSON and defstruct.
• definitions contains schemas for reuse.
• dependencies allows the schema of the map to change based on the presence of certain special properties
• description of the schema.
• else see if, then, else.
• enum specifies an enumeration
• examples the value of this keyword must be an array. There are no restrictions placed on the values within the array.
• exclusive_maximum is a boolean. When true, it indicates that the range excludes the maximum value.
• exclusive_minimum is a boolean. When true, it indicates that the range excludes the minimum value.
• format semantic validation.
• id a unique identifier.
• if, then, else: These keywords work together to implement conditional application of a subschema based on the outcome of another subschema.
• items specifies the type(s) of the items.
• keys could be :atoms or :strings.
• max_items the maximum length of list.
• max_length the maximum length of string.
• max_properties the maximum count of properties for the map.
• maximum the maximum value.
• min_items the minimal length of list.
• min_length the minimal length of string.
• min_properties the minimal count of properties for the map.
• minimum the minimum value.
• module the module of a struct.
• multiple_of is a number greater 0. The value has to be a multiple of this number.
• not negates the given schema
• one_of the given data must be valid against exactly one of the given subschemas.
• pattern_properties specifies schemas for properties by patterns
• pattern restrict a string to a particular regular expression.
• properties specifies schemas for properties.
• property_names a schema to check property names.
• ref a reference to a schema.
• required contains a set of required properties.
• schema declares the used schema.
• title of the schema.
• then see if, then, else
• type specifies the data type for a schema.
• unique_items disallow duplicate items, if set to true.
• validator a custom validator. This can be a function, a tuple with module and function name, or a Xema.Validator behaviour.

@type type() ::
  :any
  | :atom
  | :boolean
  | false
  | :float
  | :integer
  | :keyword
  | :list
  | :map
  | nil
  | :number
  | :string
  | :struct
  | true
  | :tuple

The type for the schema.