tmux chain keyboard shortcuts, or equivalent for screen's `bind -c` + `command -c`

One nice feature of screen is its ability to assign keyboard shortcuts to groups called "classes". With bind -c, you could assign that shortcuts to a particular class, and binding command -c to a key allowed you to select that class. This allowed multi-tier keyboard shortcuts. For example, I used the x key to select a class dedicated common commands. By having these launcher shortcuts in their own class, it is possible to use mnemonic keys without worrying about conflicts with the normal set of key-bindings. Is there any way to replicate this feature in tmux?

Example

# from my .screenrc
bind -c execute o screen -t imap 10 offlineimap.sh -o
bind -c execute m screen -t mpd ncmpcpp
bind -c execute w screen -t vw vimwiki
# ... more application launchers 
bind x command -c execute

Usage: prefixx enters the launcher key class, where I put all my application keyboard shortcuts.

Answer

After understanding better what you are trying to do, I think a short bash script is the best way to go (sorry, I don't think a tmux-only solution similar to screen command classes exists):

In .tmux.conf:

bind-key x command-prompt -p "launch what?" " "run-shell \"tmux-launcher %%\""

tmux-launcher should be an executable shell script somewhere in your path:

#!/bin/bash
case $1 in 
  o) tmux new-window -n imap -t 10 offlineimap.sh -o ;;
  m) tmux new-window -n mod ncmpcpp ;;
  w) tmux new-window -n vw vimwiki ;;
esac

One drawback is that you must type return after the letter that selects the window to create.