Give example values for CSS rules in embedding

app/assets/javascripts/admin/components/embedding-setting.js.es6

@@ -6,6 +6,11 @@ export default Ember.Component.extend({
   @computed('field')
   inputId(field) { return field.dasherize(); },
 
+  @computed('placeholder')
+  placeholderValue(placeholder) {
+    return placeholder ? I18n.t(placeholder) : null;
+  },
+
   @computed('field')
   translationKey(field) { return `admin.embedding.${field}`; },
 

app/assets/javascripts/admin/templates/components/embedding-setting.hbs

@@ -5,7 +5,7 @@
   </label>
 {{else}}
   <label for={{inputId}}>{{i18n translationKey}}</label>
-  {{input value=value id=inputId}}
+  {{input value=value id=inputId placeholder=placeholderValue}}
 {{/if}}
 
 <div class='clearfix'></div>

app/assets/javascripts/admin/templates/embedding.hbs

@@ -46,8 +46,13 @@
     <h3>{{i18n "admin.embedding.crawling_settings"}}</h3>
     <p class="description">{{i18n "admin.embedding.crawling_description"}}</p>
 
-    {{embedding-setting field="embed_whitelist_selector" value=embedding.embed_whitelist_selector}}
-    {{embedding-setting field="embed_blacklist_selector" value=embedding.embed_blacklist_selector}}
+    {{embedding-setting field="embed_whitelist_selector"
+                        value=embedding.embed_whitelist_selector
+                        placeholder="admin.embedding.whitelist_example"}}
+
+    {{embedding-setting field="embed_blacklist_selector"
+                        value=embedding.embed_blacklist_selector
+                        placeholder="admin.embedding.blacklist_example"}}
   </div>
 
   <div class='embedding-secondary'>

config/locales/client.en.yml

@@ -2592,7 +2592,9 @@ en:
         embed_username_key_from_feed: "Key to pull discourse username from feed"
         embed_truncate: "Truncate the embedded posts"
         embed_whitelist_selector: "CSS selector for elements that are allowed in embeds"
+        whitelist_example: "article, #story, .post"
         embed_blacklist_selector: "CSS selector for elements that are removed from embeds"
+        blacklist_example: ".ad-unit, header"
         feed_polling_enabled: "Import posts via RSS/ATOM"
         feed_polling_url: "URL of RSS/ATOM feed to crawl"
         save: "Save Embedding Settings"