improve documentation thanks @jerome

README.md

@@ -9,7 +9,7 @@ Gadget api is similar to any renderjs field api.
 ```javascript
 gadget.render({
   key: 'field_identificator',
-  value: [1,2],
+  value: [1,2], // json_document
   schema: {
     type: 'array',
     items: {
@@ -26,6 +26,8 @@ If schema_url is specified instead of schema property then schema_url is used fo
 Schema_url parameter should be specified for proper computation of an absolute url. If schema_url is omitted
 then the current gadget url is used as base_url.
 
+gadget.getContent() can be used to get the current value of edited json document.
+
 Parent gadget should have declared notification methods to catch validation status.
 
 ```javascript
@@ -65,7 +67,127 @@ rJS(window)
   })
 ``` 
 
-## What inside
+## rendering rules 
+
+* string json schema type is rendered as `<input type="string">`
+
+* number/integer json schema type is rendered as `<input type="number">`
+
+  for integer step=1 is set by default 
+  
+  this step can be changed by using multipleOf property
+  
+  html5 attributes min/max is used to limit the value
+
+* enum is rendered as a select
+
+```json
+{"enum": ["Street", "Avenue", "Boulevard"]}
+``` 
+
+is rendered as select :
+
+```html
+<select>
+  <option value="Street">Street</option>
+  <option value="Avenue">Avenue</option>
+  <option value="Boulevard">Boulevard</option>
+</select>
+```
+
+* set of oneOf/anyOf const schema with titles render as select with titles:
+
+json schema:
+
+```json
+{"oneOf": [
+  {
+    "title": "Street - small road",
+    "const": "Street"
+  },
+  {
+    "title": "Avenue - larger road. This is the recommended option",
+    "const": "Avenue"
+  },
+  {
+    "title": "Boulevard",
+    "const": "Boulevard"
+  }
+]}
+```
+
+json document:
+
+```json
+"Avenue"
+```
+
+is rendered as select:
+
+```html
+<select>
+  <option value="Street">Street - small road</option>
+  <option selected value="Avenue">Avenue - larger road. This is the recommended option</option>
+  <option value="Boulevard">Boulevard</option>
+</select>
+```
+
+* json_document strongly react to render so:
+
+schema
+```json
+{
+  "$schema": "http://json-schema.org/draft-06/schema#",
+  "title": "event",
+  "type": "object",
+  "additionalProperties": false,
+  "properties": {
+    "time": {"type": "integer"},
+    "contact": {
+      "anyOf": [
+        {
+          "title": "organisation",
+          "type": "object",
+          "additionalProperties": false,
+          "properties": {
+            "type": {"const": "organisation", "default": "organisation"},
+            "title": {"type": "string"},
+            "corporate_registration_code": {"type": "string"}
+          }
+        },
+        {
+          "title": "person",
+          "type": "object",
+          "additionalProperties": false,
+          "properties": {
+            "type": {"const": "person", "default": "person"},
+            "title": {"type": "string"},
+            "marital_status": {"enum": ["married", "divorced", "single"]}
+          }
+        }
+      ]
+    }
+  }
+}
+```
+
+if json_document = undefined then the it is rendered as: 
+
+![event undefined](doc/event_document_undefined.png)
+
+and clicking on selector:
+
+![event undefined_pressed](doc/event_with_pressed_selector.png)
+
+if json_document = `{"contact":{"type":"person"}}` then it's rendered as:
+
+![event_person](doc/event_person.png)
+
+if json_document = `{"contact":{"type":"organisation"}}` then it's rendered as:
+
+![event_organisation](doc/event_organisation.png)
+
+## What is inside
 
 gadget consists of three parts: