Updated Plugin development (markdown)

Plugin-development.md

@@ -41,4 +41,31 @@ The constructor gets the WebSlides instance which allows you to call any of the
 
 ### Plugins that affect only some slides
 
-There are times in which you may need to add a feature to only certain slides like we do with videos for example.
+There are times in which you may need to add a feature to only certain slides like we do with videos for example. Since plugins have access to the `WebSlides` instance and that has access to the `el` which holds all of the slides, the recommended approach is to `querySelectorAll` the elements that interest you:
+
+```javascript
+class MyPlugin {
+  constructor(wsInstance) {
+    const elements = wsInstance.el
+        .querySelectorAll('[data-my-interesting-elements]');
+  }
+}
+```
+
+And then use in conjunction with `Slide.getSectionFromEl` and the [events](Core-Api#events-1) that the Slides provide:
+
+```javascript
+class MyPlugin {
+  constructor(wsInstance) {
+    const elements = wsInstance.el
+      .querySelectorAll('[data-my-interesting-elements]');
+
+    elements.forEach(element => {
+      const {i} = Slide.getSectionFromEl(element);
+      const slide = wsInstance.slides[i - 1];
+
+      slide.el.addEventListener('slide:enable', MyPlugin.onSectionEnabled);
+    });
+  }
+}
+```