Add documentation page for schema validator

Author: rvsia

packages/react-renderer-demo/src/app/pages/renderer/renderer-api.md

@@ -30,6 +30,7 @@ Form Renderer provides a lot of customization via props.
 |onCancel|func|A cancel callback, which receives `values` as the first argument.||
 |debug|func|A function which will be called with every form update, i.e. `({ values }) => setValues(values)`, please take a look [here](https://final-form.org/docs/react-final-form/types/FormProps#debug)||
 |initialValues|object|An object of fields names as keys and values as their values.||
+|[schemaValidatorMapper](/renderer/schema-validator)|object|Schema validators mapper. You can control schemas of your components, validators and actions.||
 |subscription|object|You can pass your own [subscription](https://final-form.org/docs/react-final-form/types/FormProps#subscription), which will be added to default settings.|`{ pristine: true, submitting: true, valid: true }`|
 |[validate](/renderer/validators)|func|A function which receives all form values and returns an object with errors.||
 |[validatorMapper](/renderer/validators#validatormapper)|object|A mapper containing custom validators, it's automatically merged with the default one.||

packages/react-renderer-demo/src/app/pages/renderer/schema-validator.md

@@ -0,0 +1,60 @@
+import Grid from '@material-ui/core/Grid'
+
+import ListOfContents from '../../src/helpers/list-of-contents';
+
+<Grid container item>
+<Grid item xs={12} md={10}>
+
+# Schema validation
+
+Data Driven Forms contains default schema validator, that controls basic schema attributes: `name`, `component`, conditions, validators, etc. If you want to control your own validators, components or actions, use [schemaValidatorMapper](/renderer/renderer-api#optionalprops) prop.
+
+It's a simple object containing three keys: `components`, `actions`, `validators`. Each of these is an another object with names as keys and functions as returns. Components' validators receive the whole field object, actions'/validators' validators receive two arguments: action/validator as the first one and the name of the field as the second one.
+
+For returning an error please use `DefaultSchemaError` imported from the renderer's package. If the schema is correct, do nothing.
+
+## Example
+
+```jsx
+import FormRenderer, { DefaultSchemaError } from '@data-driven-forms/react-form-renderer';
+
+const schemaValidatorMapper = {
+    components: {
+        // schema validators for components
+        [component]: (field) => {
+            if(someError(field)) {
+                throw new DefaultSchemaError(`Error message in field ${field.name}`);
+            }
+        }
+    },
+    actions: {
+        // schema validators for actions
+        [actionName]: (action, fieldName) => {
+            if(someError(action)) {
+                throw new DefaultSchemaError(`Error message in field ${fieldName}`);
+            }
+        }
+    },
+    validators: {
+        // schema validators for validators
+        [validatorType]: (validator, fieldName) => {
+            if(someError(validator)) {
+                throw new DefaultSchemaError(`Error message in field ${fieldName}`);
+            }
+        }
+    }
+}
+
+...
+
+<FormRenderer
+    {...props}
+    schemaValidatorMapper={schemaValidatorMapper}
+/>
+```
+
+</Grid>
+<Grid item xs={false} md={2}>
+  <ListOfContents file="renderer/schema-validator" />
+</Grid>
+</Grid>

packages/react-renderer-demo/src/app/src/components/navigation/documentation-pages.js

@@ -63,6 +63,10 @@ export const docs = [
     component: 'field-array',
     linkText: 'FieldArray Provider'
   },
+  {
+    component: 'schema-validator',
+    linkText: 'Schema validation'
+  },
   {
     component: 'migration-guide',
     linkText: 'Migration guide 1.x to 2.x'