Merge pull request #466 from lcdservices/patch-1

CRM-21020 add additional params and example

docs/hooks/hook_civicrm_alterMailContent.md

@@ -15,4 +15,21 @@ tokenizing it.
 
 ## Details
 
--   $content - fields include: html, text, subject
\ No newline at end of file
+-   $content - fields include: html, text, subject, groupName, valueName, messageTemplateID
+
+## Example
+
+```php
+   /**
+    * Implement hook_civicrm_alterMailContent
+    *
+    * Replace invoice template with custom content from file
+    */
+  function mail_civicrm_alterMailContent(&$content) {
+    if (CRM_Utils_Array::value('valueName', $content) == 'contribution_invoice_receipt') {
+      $path = CRM_Core_Resources::singleton()->getPath('org.myorg.invoice');
+      $html = file_get_contents($path.'/msg/contribution_invoice_receipt.html.tpl');
+      $content['html'] = $html;
+    }
+  }
+```