docs: Extend readme with info about strict mode

Author: DannyvdSluijs

README.md

@@ -4,7 +4,12 @@
 [![Latest Stable Version](https://poser.pugx.org/justinrainbow/json-schema/v/stable)](https://packagist.org/packages/justinrainbow/json-schema)
 [![Total Downloads](https://poser.pugx.org/justinrainbow/json-schema/downloads)](https://packagist.org/packages/justinrainbow/json-schema/stats)
 
-A PHP Implementation for validating `JSON` Structures against a given `Schema` with support for `Schemas` of Draft-3 or Draft-4. Features of newer Drafts might not be supported. See [Table of All Versions of Everything](https://json-schema.org/specification-links.html#table-of-all-versions-of-everything) to get an overview of all existing Drafts.
+A PHP Implementation for validating `JSON` Structures against a given `Schema` with support for `Schemas` of Draft-3, 
+Draft-4 or Draft-6. 
+
+Features of newer Drafts might not be supported. See [Table of All Versions of Everything](https://json-schema.org/specification-links.html#table-of-all-versions-of-everything) to get an overview 
+of all existing Drafts.
+
 
 See [json-schema](http://json-schema.org/) for more details.
 
@@ -187,24 +192,25 @@ A number of flags are available to alter the behavior of the validator. These ca
 third argument to `Validator::validate()`, or can be provided as the third argument to
 `Factory::__construct()` if you wish to persist them across multiple `validate()` calls.
 
-| Flag | Description |
-|------|-------------|
-| `Constraint::CHECK_MODE_NORMAL` | Validate in 'normal' mode - this is the default |
-| `Constraint::CHECK_MODE_TYPE_CAST` | Enable fuzzy type checking for associative arrays and objects |
-| `Constraint::CHECK_MODE_COERCE_TYPES` | Convert data types to match the schema where possible |
-| `Constraint::CHECK_MODE_EARLY_COERCE` | Apply type coercion as soon as possible |
-| `Constraint::CHECK_MODE_APPLY_DEFAULTS` | Apply default values from the schema if not set |
-| `Constraint::CHECK_MODE_ONLY_REQUIRED_DEFAULTS` | When applying defaults, only set values that are required |
-| `Constraint::CHECK_MODE_EXCEPTIONS` | Throw an exception immediately if validation fails |
-| `Constraint::CHECK_MODE_DISABLE_FORMAT` | Do not validate "format" constraints |
-| `Constraint::CHECK_MODE_VALIDATE_SCHEMA` | Validate the schema as well as the provided document |
-
-Please note that using `CHECK_MODE_COERCE_TYPES` or `CHECK_MODE_APPLY_DEFAULTS` will modify your
+| Flag                                            | Description                                                     |
+|-------------------------------------------------|-----------------------------------------------------------------|
+| `Constraint::CHECK_MODE_NORMAL`                 | Validate in 'normal' mode - this is the default                 |
+| `Constraint::CHECK_MODE_TYPE_CAST`              | Enable fuzzy type checking for associative arrays and objects   |
+| `Constraint::CHECK_MODE_COERCE_TYPES` [^1][^2]  | Convert data types to match the schema where possible           |
+| `Constraint::CHECK_MODE_EARLY_COERCE` [^2]      | Apply type coercion as soon as possible                         |
+| `Constraint::CHECK_MODE_APPLY_DEFAULTS` [^1]    | Apply default values from the schema if not set                 |
+| `Constraint::CHECK_MODE_ONLY_REQUIRED_DEFAULTS` | When applying defaults, only set values that are required       |
+| `Constraint::CHECK_MODE_EXCEPTIONS`             | Throw an exception immediately if validation fails              |
+| `Constraint::CHECK_MODE_DISABLE_FORMAT`         | Do not validate "format" constraints                            |
+| `Constraint::CHECK_MODE_VALIDATE_SCHEMA`        | Validate the schema as well as the provided document            |
+| `Constraint::CHECK_MODE_STRICT` [^3]            | Validate the scheme using strict mode using the specified draft | 
+
+[^1]: Please note that using `CHECK_MODE_COERCE_TYPES` or `CHECK_MODE_APPLY_DEFAULTS` will modify your
 original data.
-
-`CHECK_MODE_EARLY_COERCE` has no effect unless used in combination with `CHECK_MODE_COERCE_TYPES`. If
+[^2]: `CHECK_MODE_EARLY_COERCE` has no effect unless used in combination with `CHECK_MODE_COERCE_TYPES`. If
 enabled, the validator will use (and coerce) the first compatible type it encounters, even if the
 schema defines another type that matches directly and does not require coercion.
+[^3]: `CHECK_MODE_STRICT` only can be used for Draft-6 at this point.
 
 ## Running the tests