New Page: Form Validation

src/_data/toc/frontend-developer-guide.yml

@@ -178,6 +178,9 @@ pages:
         - label: Example theme translation dictionary
           url: /frontend-dev-guide/translations/translate_practice.html
 
+    - label: Form validation
+      url: /frontend-dev-guide/validations/form-validation.html
+
     - label: Tools
       include_versions: ["2.2", "2.3"]
       url: /frontend-dev-guide/tools/tools_overview.html

src/guides/v2.2/frontend-dev-guide/validations/form-validation.md

@@ -0,0 +1,26 @@
+---
+group: frontend-developer-guide
+title: Form validation
+contributor_name: Adarsh Manickam
+contributor_link: https://github.com/drpayyne
+functional_areas:
+  - Frontend
+---
+
+The Magento application provides various ways to validate your form inputs. This implementation is based, and extends, [jQuery Validation](https://jqueryvalidation.org/documentation).
+
+## Validation Module Structure
+
+There are three main validation modules present in Magento: `jquery/validate`, `mage/validation`, and `mage/validation/validation`.
+
+#### `jquery/validate`
+
+This is an alias for [`lib/web/jquery/jquery.validate`]({{ site.mage2bloburl }}/{{ page.guide_version }}/lib/web/jquery/jquery.validate.js). This is the base validation JavaScript file provided by jQuery that Magento extends.
+
+#### `mage/validation`
+
+This module is present at [`lib/web/mage/validation.js`]({{ site.mage2bloburl }}/{{ page.guide_version }}/lib/web/mage/validation.js). This module includes `jquery/validate` and adds various functions, such as `$.validator.addMethod`, which can be used by mixins to add custom validation rules, a base set of rules to validate, the `mage.validation` widget, and more. 
+
+#### `mage/validation/validation`
+
+This module is present at [`lib/web/mage/validation/validation.js`]({{ site.mage2bloburl }}/{{ page.guide_version }}/lib/web/mage/validation/validation.js). This is considered the entry point for the form validator in Magento and is aliased as `validation` at [`Magento_Theme/view/frontend/requirejs-config.js`]({{ site.mage2bloburl }}/{{ page.guide_version }}/app/code/Magento/Theme/view/frontend/requirejs-config.js#L29). This includes `mage/validation` (which in turn includes `jquery/validate`), and adds a few more rules to the validator.

src/guides/v2.3/frontend-dev-guide/validations/form-validation.md

@@ -0,0 +1 @@
+../../../v2.2/frontend-dev-guide/validations/form-validation.md