I use "Todo Tree" in VS Code which is one of my mandatory extensions wherever I go. Super useful for not only tag highlighting, but as a general bookmark system inside the codebase.

[0]: https://marketplace.visualstudio.com/items?itemName=Gruntfug...

In addition, Vim does it by default for many filetypes. And it's easy to add for ones that don't. Other editors/IDEs probably also have it – overall I'd say it's a common feature.