Deprecate limited-use and potentially confusing [class] BBCode tag

- Replace its usage in Mastodon emoji with an internal tag [emoji]

doc/BBCode.md

@@ -650,10 +650,4 @@ On Mastodon this field is used for the content warning.
 [style=text-shadow: 0 0 4px #CC0000;]You can change all the CSS properties of this block.[/style]</td>
   <td><span style="text-shadow: 0 0 4px #cc0000;;">You can change all the CSS properties of this block.</span></td>
 </tr>
-<tr>
-  <td>Custom class block<br>
-<br>
-[class=custom]If the class exists, this block will have the custom class style applied.[/class]</td>
-  <td><pre>&lt;span class="custom"&gt;If the class exists,<br> this block will have the custom class<br> style applied.&lt;/span&gt;</pre></td>
-</tr>
 </table>

doc/de/BBCode.md

@@ -609,13 +609,5 @@ Dieses Feld wird von Mastodon für die Inhaltswarnung (content warning) verw
 [style=text-shadow: 0 0 4px #CC0000;]Du kannst alle CSS-Eigenschaften eines Blocks &auml;ndern-[/style]</td>
   <td><span style="text-shadow: 0 0 4px #cc0000;;">Du kannst alle CSS-Eigenschaften eines Blocks &auml;ndern-</span></td>
 </tr>
-<tr>
-  <td>Benutzerdefinierte CSS Klassen<br>
-<br>
-[class=custom]Wenn die vergebene Klasse in den CSS Anweisungen existiert, wird sie angewandt.[/class]</td>
-  <td><pre>&lt;span class="custom"&gt;Wenn die<br>
-vergebene Klasse in den CSS Anweisungen<br>
-existiert,wird sie angewandt.&lt;/span&gt;</pre></td>
-</tr>
 </table>
 

src/Content/Text/BBCode.php

@@ -1648,7 +1648,11 @@ class BBCode
 				// Check for style sheet commands
 				$text = preg_replace("(\[style=(.*?)\](.*?)\[\/style\])ism", '<span style="$1">$2</span>', $text);
 
+				// Mastodon Emoji (internal tag, do not document for users)
+				$text = preg_replace("(\[emoji=(.*?)](.*?)\[/emoji])ism", '<span class="mastodon emoji"><img src="$1" alt="$2" title="$2"/></span>', $text);
+
 				// Check for CSS classes
+				// @deprecated since 2021.12, left for backward-compatibility reasons
 				$text = preg_replace("(\[class=(.*?)\](.*?)\[\/class\])ism", '<span class="$1">$2</span>', $text);
 
 				// handle nested lists

src/Protocol/ActivityPub/Processor.php

@@ -96,7 +96,7 @@ class Processor
 			array_combine(
 				array_column($emojis, 'name'),
 				array_map(function ($emoji) {
-					return '[class=emoji mastodon][img=' . $emoji['href'] . ']' . $emoji['name'] . '[/img][/class]';
+					return '[emoji=' . $emoji['href'] . ']' . $emoji['name'] . '[/emoji]';
 				}, $emojis)
 			)
 		);