A simple trick to decorate Theorem-like environments with poker suits QED symbols.
I did not come up with this theorem decoration style (I've first seen it here) nor with the whole code (I salvaged it from TeX StackExchange and other sources over the years). This is just my current implementation of the code.
This example is a LuaTeX-based plain TeX project which implements a LuaTeX callback function to show the components of a typeset paragraph. It is designed to accompany a blog post and, for simplicity, it is not a full-blown “parser”—for example, it is not recursive and ignores a number of node types. However, it offers a useful starting point for anyone wishing to explore callbacks in more detail.
The changes package, distributed with TeX Live, allows the user to manually markup changes of text, such as additions, deletions, or replacements. This example customizes the package to show author annotations with avatars. (Here's a more conventional example without the avatars. )
The changes package, distributed with TeX Live, allows the user to manually markup changes of text, such as additions, deletions, or replacements. Changed text is shown in a different colour; deleted text is crossed out. The package allows definition of additional authors and their associated colour. It also allows you to define a markup for authors or annotations. (Here's another customised example using avatars for the author annotations.)