Import "Extending Smarty" wiki page

https://wiki.civicrm.org/confluence/display/CRMDOC/Extending+Smarty

docs/framework/templates/extending-smarty.md

+# Extending Smarty
+
+The Smarty templating language that is used to output the HTML for
+CiviCRM's templates is fairly powerful in its own right, but sometimes
+it can't do everything you want.  Smarty can be extended using "plugins"
+-- you can find some examples and documentation online at [Smarty's
+website](http://www.smarty.net){.external-link} or by searching the web.
+
+To install Smarty plugins without editing CiviCRM core (which is
+difficult to maintain), you will have to implement the
+hook_civicrm_config hook.  (Activating hooks in Drupal and Joomla is
+covered
+[here](http://wiki.civicrm.org/confluence/display/CRMDOC/CiviCRM+hook+specification#CiviCRMhookspecification-Proceduresforimplementinghooks%28forDrupal%29)).
+
+Once you've created your module or hook file, you can retrieve the
+Smarty object and register your custom plugin path:
+
+<div class="code panel" style="border-width: 1px;">
+
+<div class="codeContent panelContent">
+
+    function yourmodule_civicrm_config(&$config) {
+        $smarty = CRM_Core_Smarty::singleton();
+        array_push($smarty->plugins_dir, __DIR__ . '/relative/path/to/custom/plugin/directory');
+    }
+
+</div>
+
+</div>
+
+Then in that custom plugin directory, you can place whatever Smarty
+plugins you need.
+
+You can also use this trick to change other Smarty behavior, such as
+whether it can evaluate PHP placed directly in templates. For instance:
+
+<div class="code panel" style="border-width: 1px;">
+
+<div class="codeContent panelContent">
+
+    function yourmodule_civicrm_config(&$config) {
+        $smarty = CRM_Core_Smarty::singleton();
+        array_push($smarty->security_settings['MODIFIER_FUNCS'], 'explode'); // allow the explode() php function to be used as a "modifier" in Smarty templates
+    }
+
+</div>
+
+</div>
+
+However, be very careful with these settings – if you don't know what
+you're doing, you can open security holes or create a mess of code
+that's difficult to maintain.

mkdocs.yml

@@ -88,6 +88,7 @@ pages:
   - Template Reference:
     - Templates: framework/templates/index.md
     - Customizing templates: framework/templates/customizing.md
+    - Extending Smarty: framework/templates/extending-smarty.md
   - PseudoConstant Reference: framework/pseudoconstant.md
   # Other Reference:
   # CiviMail: /reference/civimail.md

redirects/wiki-crmdoc.txt

@@ -179,3 +179,4 @@ Backbone+Reference framework/backbone
 Extensions+and+Permissions security/permissions#extensions
 Customize+Built-in+Profile+Contribution+and+Event+Registration+Screens framework/templates/customizing
 Page+Templates framework/templates
+Extending+Smarty framework/templates/extending-smarty