Validation: Elaborate on abstract

Author: awwright

jsonschema-validation.xml

@@ -41,11 +41,13 @@
 
         <abstract>
             <t>
-                JSON Schema (application/schema+json) has several purposes, one of which is JSON instance
-                validation. This document specifies a vocabulary for JSON Schema to make assertions about
-                valid instances.
+                JSON Schema (application/schema+json) has several purposes, one of which is JSON instance validation.
+                This document specifies a vocabulary for JSON Schema to describe the meaning of JSON documents,
+                provide hints for user interfaces working with JSON data,
+                and to make assertions about what a valid document must look like.
             </t>
         </abstract>
+
         <note title="Note to Readers">
             <t>
                 The issues list for this draft can be found at <eref target="https://github.com/json-schema-org/json-schema-spec/issues"/>.