diff --git a/Gemfile b/Gemfile
index a1dda40..5f9e9b0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,3 @@
 source "https://rubygems.org"
-ruby '2.4.6'
+ruby '2.4.7'
 gemspec
diff --git a/src/_posts/2019-08-30-civicrm-mailing-validation.md b/src/_posts/2019-08-30-civicrm-mailing-validation.md
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@@ -0,0 +1,129 @@
+---
+layout: post
+title: CiviCRM AngularJS extension
+description: Adding custom validation to the CiviCRM Mailing form
+image: civicrm_validation_header.jpg
+category: howto
+date: 2019-08-30
+---
+
+We support [Campaign Against Arms Trade](https://caat.org.uk), a right-on group
+that works to end the international arms trade, with their technology –
+including CiviCRM](https://civicrm.org/), a popular open source
+"constituent relationship management" platform. 
+
+Among other things, CAAT uses CiviCRM's "Mailing" features to send out emails to
+their supporters, and they told us that they're experiencing an annoying bug: if
+a user sends out a mailing with the same name (not subject line, just the
+internal identifier 🙄) as an existing one, it'll cause the CRM to freeze up
+elsewhere.
+
+As an added challenge, the mailing features of CiviCRM [now use
+AngularJS](https://docs.civicrm.org/dev/en/latest/framework/angular/) following
+a recent rebuild by the developers, and there aren't many tutorials or examples
+out there to customise it. Luckily, the CiviCRM developer community was
+super-helpful, and we managed to sort out some in-form validation to prevent
+duplicate mailing names for our client… and now for you, too!
+
+## Create a new extension
+
+Using [`civix`](https://github.com/totten/civix), we set up a new CiviCRM extension for our code:
+
+    civix generate:module mailing
+
+(We called our extension `mailing`, because our creative director was occupied
+with an Art at the time)
+
+Our client sensibly keeps their custom CiviCRM extensions in `git`, so at this
+stage we initialised a repository, added the boilerplate template code, and
+pushed.
+
+## Set up the AngularJS hook
+
+A function called `mailing_civicrm_alterAngular()`  will get executed whenever
+an AngularJS page loads, and you can use a `ChangeSet` to edit an AngularJS
+template. Because AngularJS templates specify form logic, this also lets you
+change the validation behaviour. Our hook function looks like this:
+
+    function mailing_civicrm_alterAngular($angular) {
+      $changeSet = \Civi\Angular\ChangeSet::create('mailing_name_unique')
+        ->alterHtml('~/crmMailing/BlockSummary.html', function(phpQueryObject $doc) {
+          // name validation
+          $doc->find('.crm-group:has([crm-ui-id="subform.mailingName"])')->attr('ng-controller', 'NameValidateCtrl');
+          $doc->find('[crm-ui-id="subform.mailingName"]')->attr('ng-blur', 'validateName(mailing, \'name\')');
+          $doc->find('[crm-ui-id="subform.mailingName"]')->attr('crm-ui-validate', 'isValid');
+        });
+
+      $angular->add($changeSet);
+
+      CRM_Core_Resources::singleton()->addScriptFile('mailing', 'js/disallow-duplicate-names.js');
+    }
+
+
+Setting `crm-ui-validate` to `validateName` directly fired the event _way_ too
+many times, so instead `validateName` is only called when focus leaves the
+field, `ng-blur`, which then sets the `isValid` variable that's checked by
+`crm-ui-validate`.
+
+## Create the `validateName` function
+
+Then, the code which queries the CiviCRM API to check for mailings with
+duplicate names:
+
+    var validating = false;
+    
+    (function(angular, $) {
+      var crmMailing = angular.module('crmMailing');
+    
+      crmMailing.controller('NameValidateCtrl', function($scope) {
+          $scope.isValid = false;
+    
+          $scope.validateName = function(mailing, field) {
+            if (!validating) {
+              validating = true;
+    
+              CRM.api3('Mailing', 'get', {
+                "sequential": 1,
+                "name": mailing[field],
+                "id": {"!=": mailing.id}
+              }).then(function(result) {
+                // do something with result
+                if (result.count > 0 ) {
+                  $scope.isValid = false;
+                  CRM.alert(ts('There is already a mailing with this name; sending this one will crash CiviCRM!'));
+                } else {
+                  $scope.isValid = true;
+                }
+              }, function(error) {
+                // oops
+                console.log(error);
+              });
+    
+              validating = false;
+          }
+        };
+      });
+    })(angular, CRM.$);
+
+(saved as `js/disallow-duplicate-names.js`)
+
+## Conclusion
+
+Activate the extension, e.g. with `cv`
+
+     $ cv en mailing
+
+Now, open a mailing and try to give it the same name as an existing one – you
+should see the field border turn red, and you'll be prevented from continuing or
+sending the mailing:
+
+!["Mailing name" field showing the field with a red border and red label](/assets/images/2019-08-30_civicrm_validation.png)
+
+(As a bonus, the extension also sends a notification to the user using
+`CRM.alert` to explain the error)
+
+It does seem like a red border sometimes hangs around the field label even after
+the value is valid again… but apart from that, the feature is working great!
+
+Lastly, props to CAAT for being a great member of the CiviCRM community and
+supporting us writing this post to share our work with y'all.
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