Added example on how to adjust the validation message for specific form field

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

@@ -50,3 +50,49 @@ define(['jquery'], function($) {
   }
 });
 ```
+
+## Modify an existing validation message
+
+It is possible to adjust the existing error message for form fields.
+This is implemented in the core codebase in scope of the [`Magento_CatlogSearch` module]({{ site.mage2bloburl }}/{{page.guide_version}}/app/code/Magento/CatalogSearch/view/frontend/templates/advanced/form.phtml).
+
+```html
+<script>
+require([
+    "jquery",
+    "mage/mage",
+    "mage/validation"
+], function($){
+    $('#form-validate').mage('validation', {
+        errorPlacement: function (error, element) {
+            var parent = element.parent();
+            if (parent.hasClass('range')) {
+                parent.find(this.errorElement + '.' + this.errorClass).remove().end().append(error);
+            } else {
+                error.insertAfter(element);
+            }
+        },
+        messages: {
+            'price[to]': {'greater-than-equals-to': '<?= $block->escapeJs(__('Please enter a valid price range.')) ?>'},
+            'price[from]': {'less-than-equals-to': '<?= $block->escapeJs(__('Please enter a valid price range.')) ?>'}
+        }
+    });
+});
+</script>
+```
+
+The `messages` object is the one that does the job - they key is the input name and the value is a list of validation rules that should be modified for the specified input field.
+Here the rule name is the key and the validation message is the value.
+
+```js
+$('#form-to-validate').mage('validation', {
+    messages: {
+        'input-name': {
+            'validation-rule-1': 'Validation message 1',
+            'validation-rule-2': 'Validation message 2',
+        },
+    }
+});
+```
+
+This comes in handy when the error message needs to be specific but the rule does not change.