It's a custom BB Code. I guess it only works on PCs.
BB Code: spoiler (id: 13)
Title
Spoiler
BB Code Tag Name
spoiler
Replacement
<div style="margin:20px; margin-top:5px">
<div class="smallfont">Spoiler: (<i>Highlight this box to see the hidden message.</i>)</i></div></font>
<pre class="alt2" style="margin:0px; padding:$stylevar[cellpadding]px; border:1px inset; width:$stylevar[codeblockwidth]; height:{$blockheight}px; overflow:auto"><div dir="ltr" style="text-align:left;"><table bgcolor=#D5D5D5><tr><td><font color=#D5D5D5>{param}</font></td></tr></table></div></pre>
</div>
Increase Size Decrease Size
Example
Here's how the movie ends: The butler did it!
Description
The [spoiler] tag allows text to be hidden until the reader highlights the spoiler box to reveal the text.
Increase Size Decrease Size
Use {option}
Yes No
Button Image (Optional)
If you would like this BB code to appear as a clickable button on the message editor toolbar, enter the URL of an image 21 x 20 pixels in size that will act as the button to insert this BB code.
Remove Tag If Empty
Yes No
Disable BB Code Within This BB Code
Yes No
Disable Smilies Within This BB Code
Yes No
Disable Word Wrapping Within This BB Code
Yes No
Disable Automatic Link Parsing Within This BB Code
Yes No
Explanations:
Title: The title of your tag, which will be used to generate the BB code list.
Tag: This is the text for the BB code, which goes inside the square brackets.
e.g. you would use 'b' for tags, 'url' (without quotes) for [url] tags.
Replacement: This is the HTML code for the BB code replacement. Make sure that you include '{param}' (without the quotes) to insert the text between the opening and closing BB code tags, and '{option}' for the parameter within the BB code tag. You can only use {option} if 'Use Option' is set to yes.
e.g. you would use <b>{param}</b> for tags, <a href="{option}">{param}</a> for . You will always use '{param}', but you will only use '{option}' when "Use Option?" is "yes". Note that '{relpath}' can be used in replacement code to signify the path of the current page. e.g. <a href="{relpath}#{option}">{param}</a>
Example: This is a sample piece of BB code to use as an example for this particular BB code.
e.g. you would use [b]Bold for [b] tags, [url=http://www.example.com]Example Web Site (xxx) for [url] tags
Description: This is a piece of text to describe the BB code tag. This can include HTML tags if you wish.
Use Option: Setting this option to yes will allow you to create a style tag, rather than just a style tag.