For questions about spoiler blocks (text hidden until mouseover) in posts.
Spoiler blocks are used to obscure content in posts, so that it's not immediately displayed, and only displayed if the user mouses over it or taps on it. This is commonly used on sites like Movies & TV, Science Fiction & Fantasy, and Puzzling to obscure movie or game spoilers (hence the name), or hints and solutions to puzzles.
Spoiler markup functions almost like quote markup, except that it has the added functionality of spoilers. You can use it using the following markup:
>! This text is in a spoiler
The above text results in an empty quote block with the text fading in on mouseover on the desktop site and fading away once the mouse cursor is moved away; it can be clicked to show the text persistently (or clicked again to hide it again). On the mobile site and mobile app, it's replaced with a button that must be tapped to see the text. For example:
This text is in a spoiler
Use this tag for general bug reports, feature requests, and overall questions about spoilers as they pertain to their implementation on all sites. For questions about policies regarding the use of spoiler blocks, which are set by each site, ask on the respective per-site meta, unless your question affects more than one site.