docs: Add advanced topics

Author: DannyvdSluijs

_docs/advanced-topics.md

@@ -6,4 +6,65 @@ navigation:
 
 # Advanced topics
 
-This page needs to be written, want to help out? Checkout GitHub repo!
+## Validation using schema on disk
+Validation of a JSON document can be done using a schema located on disk.
+
+```php
+<?php
+
+$data = json_decode(file_get_contents('data.json'));
+
+// Validate
+$validator = new JsonSchema\Validator;
+$validator->validate($data, (object)['$ref' => 'file://' . realpath('schema.json')]);
+
+if ($validator->isValid()) {
+    echo "The supplied JSON validates against the schema.\n";
+} else {
+    echo "JSON does not validate. Violations:\n";
+    foreach ($validator->getErrors() as $error) {
+        printf("[%s] %s\n", $error['property'], $error['message']);
+    }
+}
+```
+
+## Validation using inline schema
+Validation of a JSON document can be done using a inline schema. This requires some additional setup of the schema storage
+```php
+<?php
+
+$data = json_decode(file_get_contents('data.json'));
+$jsonSchemaAsString = <<<'JSON'
+{
+  "type": "object",
+  "properties": {
+    "name": { "type": "string"},
+    "email": {"type": "string"}
+  },
+  "required": ["name","email"]
+}
+JSON;
+
+$jsonSchema = json_decode($jsonSchemaAsString);
+$schemaStorage = new JsonSchema\SchemaStorage();
+$schemaStorage->addSchema('internal://mySchema', $jsonSchema);
+$validator = new JsonSchema\Validator(
+    new JsonSchema\Constraints\Factory($schemaStorage)
+);
+$validator->validate($data, $jsonSchemaObject);
+
+if ($validator->isValid()) {
+    echo "The supplied JSON validates against the schema.\n";
+} else {
+    echo "JSON does not validate. Violations:\n";
+    foreach ($validator->getErrors() as $error) {
+        printf("[%s] %s\n", $error['property'], $error['message']);
+    }
+}
+```
+
+## Validation using online schema
+This paragraph needs to be written, want to help out? Checkout GitHub repo!
+
+## Using custom error messages
+This paragraph needs to be written, want to help out? Checkout GitHub repo!