Usually, you can designate any in-post text as a spoiler and it will appear in a small box that you can extend to show the contents. This is also very useful when posting walls of images and text, like I said. Another simpler variation is a spoiler system where designated text is highlighted in black and must be selected to be seen, but it doesn't have that added benefit of clutter reduction.We have the spoiler prefix. I did put in the sticky in the help forum to assume all threads in that section were spoilers though. Or are you meaning something that will filter out anything designated as a spoiler?
Usually, you can designate any in-post text as a spoiler and it will appear in a small box that you can extend to show the contents. This is also very useful when posting walls of images and text, like I said. Another simpler variation is a spoiler system where designated text is highlighted in black and must be selected to be seen, but it doesn't have that added benefit of clutter reduction.