@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. Values in data will be interpreted as schemas when possible. It is not recommended to put any data or schemas under this key. The data property is mainly for compatibility with JsonSchema.
• 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.