Listescape plugin

The Listescape plugin allows users to use characters in mailboxes names that would otherwise be illegal, for example:

Maildir++ layout disallows using the '.' character, since it's used internally as the hierarchy separator.
The '~' character at the beginning of the mailbox name is disallowed, because of the possibility that it gets expanded to user's home directory.
The '/' character is disallowed with all layouts (if it's not the hierarchy separator).

The Listescape plugin allows you to use all of these characters, as long as the virtual separator is changed to something else. The characters are escaped to the mailbox name as \NN hex codes.

So what would be a good hierarchy separator to use?

'.' and '/' are very commonly used and should work everywhere
'\' is used by Exchange, and should also work everywhere
'^' is used internally by Thunderbird and causes some trouble with it
others?

Examples

Allow '.' characters with Maildir++ layout when virtual hierarchy separator is changed to '/':

mail_plugins = $mail_plugins listescape

namespace private {
  separator = /
  inbox = yes
}

plugin {
  # The default escape character is '\', but you can change it.
  # Note that even here the expansion of % takes place, thus you need to 
  # use "%%" if you want to have the % sign as the escape character.
  #listescape_char = "\\"
}

Allow both '.' and '/' characters when virtual hierarchy separator is changed to '$':

mail_plugins = $mail_plugins listescape

namespace private {
  separator = $
  inbox = yes
}