add description and examples for maxLength keyword

content/2020-12/validation/maxLength.markdown

@@ -16,3 +16,49 @@ related:
   - vocabulary: format-annotation
     keyword: format
 ---
+
+The `maxLength` keyword is used to specify the maximum length of a string instance. It is used to enforce a constraint on the maximum number of characters allowed for a string instance.
+
+* Applies only to string data types.
+* Value must be a non-negative integer.
+* String length is counted in characters, not bytes.
+* Validation succeeds if the string length is less than or equal to the specified `maxLength`.
+
+## Examples
+
+{{<schema `Schema restricting string length to a maximum of 10 characters`>}}
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "string",
+  "maxLength": 10
+}
+{{</schema>}}
+
+{{<instance-pass `An instance with a string length less than or equal to 10 is valid`>}}
+"foo"
+{{</instance-pass>}}
+
+{{<instance-fail `An instance with a string length greater than 10 is invalid`>}}
+"This is an invalid string"
+{{</instance-fail>}}
+
+{{<schema `Schema allowing either a string with a maximum of 20 characters or a numeric value`>}}
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": [ "string", "number" ],
+  "maxLength": 20
+}
+
+{{</schema>}}
+
+{{<instance-pass `An instance with a string length less than or equal to 20 is valid`>}}
+"This is a valid string"
+{{</instance-pass>}}
+
+{{<instance-fail `An instance with a string length greater than 20 is invalid`>}}
+"This description is too long"
+{{</instance-fail>}}
+
+{{<instance-pass `An instance with a numeric value is valid`>}}
+55
+{{</instance-pass>}}