Question: I can't find a way to toggle mc internal editor in hex mode. [Here](http://www.tldp.org/LDP/LG/issue23/wkndmech_dec97/mc_article.html) it says to use F4 however it suggest to replace. How to do it?

Answer: 
You can open file with `F3`.  

Hex view - `F4`.  

Start edit - `F2`.
`F4` toggles hex mode in the Midnight Commander **viewer** (accessed using `F3`), not in the editor. Once in hex mode in the viewer, `F2` allows you to make changes to the file being viewed.

As you discovered, `F4` in the editor starts a search.