diff --git a/core/drupalci.yml b/core/drupalci.yml
index 30ec95c6a2..84701272db 100644
--- a/core/drupalci.yml
+++ b/core/drupalci.yml
@@ -1,7 +1,12 @@
+# This is the DrupalCI testbot build file for Drupal core.
+# Learn to make one for your own drupal.org project:
+# https://www.drupal.org/drupalorg/docs/drupal-ci/customizing-drupalci-testing
 build:
   assessment:
     validate_codebase:
       phplint: {  }
+      # Re-run composer install to ensure the dependencies resolve for the
+      # containerized PHP version.
       container_composer:
         options: ' install --prefer-dist --no-suggest --no-progress --no-interaction'
         halt-on-fail: true
@@ -11,12 +16,12 @@ build:
         # A test must pass eslinting standards check in order to continue processing.
         halt-on-fail: true
       phpcs:
+        # phpcs will use core's specified version of Coder.
         sniff-all-files: false
         halt-on-fail: false
-        coder-version: ^8.2@stable
     testing:
       # run_tests task is executed several times in order of performance speeds.
-      # halt-on-fail is set on the run_tests tasks in order to fail fast
+      # halt-on-fail is set on the run_tests tasks in order to fail fast.
       # suppress-deprectaions is false in order to be alerted to usages of
       # deprecated code.
       run_tests.phpunit:
@@ -39,10 +44,14 @@ build:
         testgroups: '--all'
         suppress-deprecations: false
         halt-on-fail: true
+      # Functional JavaScript tests require a concurrency of 1 because there is
+      # only one instance of PhantomJS on the testbot machine.
       run_tests.javascript:
         concurrency: 1
         types: 'PHPUnit-FunctionalJavascript'
         testgroups: '--all'
         suppress-deprecations: false
         halt-on-fail: true
-      nightwatchjs: {  }
+      # Run nightwatch testing.
+      # @see https://www.drupal.org/project/drupal/issues/2869825
+      nightwatchjs: