Although I can use things like the .hidden file to hide files even if they don't start with a period, there doesn't seem to be any way to SHOW a file even if it does start with a period.  

There are certain files (not created by me) which, despite being hidden with a period at the front, I still actually access fairly frequently (eg, .ssh, .config), and I'd like to be able to see them in the normal file list without enabling "show hidden files" which also clutters my home directory with tons of other files I don't want to see.

Simple options here would be to either have a .visible file that works the opposite of the .hidden file, or follow things like .gitignore syntax and allow a ! at the beginning of the line in the .hidden file to reverse it?  

There may already be a standard for this in other apps but I've had trouble finding any real documentation about .hidden files in general...

If a preferred option is given, I can make an attempt at implementing it myself, although a pointer in the direction of what code actually implements the .hidden file logic would be handy as it's not appearing obviously searching the codebase...