Allow marks to use merge when using template-based config

Author: engram-design

docs/template-guides/modify-nodes.md

@@ -75,6 +75,23 @@ So far, all the overrides we've done have completely replaced the attributes on
 
 Importantly, the Paragraph node actually outputs a `text-left`, `text-right`, etc class depending on the alignment in the editor. Without `merge` set, our custom class would completely replace these clases, losing our alignment functionality.
 
+You can also use `merge` for marks.
+
+```twig
+{{ entry.vizyField.renderHtml({
+    paragraph: {
+        marks: {
+            link: {
+                merge: true,
+                attrs: {
+                    class: 'text-xl',
+                },
+            },
+        },
+    },
+}) }}
+```
+
 ## Using PHP
 Alternatively, you can use the PHP method from a plugin or module to control this behaviour as well.
 

src/models/NodeCollection.php

@@ -186,7 +186,10 @@ private function _prepNodesForHtml($config = [])
                             $markConfig = $marksConfig[$mark->getType()] ?? [];
 
                             if ($markConfig) {
-                                Craft::configure($mark, $markConfig);
+                                // Check if we want to merge attributes, instead of replace. Useful for attrs.
+                                $merge = ArrayHelper::remove($markConfig, 'merge');
+
+                                self::configure($mark, $markConfig, $merge);
                             }
                         }
                     }