<item>! -- refers to your <ref id="spoolfile" name="$spoolfile"> (incoming) mailbox
<item>> -- refers to your <ref id="mbox" name="$mbox"> file
<item>< -- refers to your <ref id="record" name="$record"> file
+<item>^ -- refers to the current mailbox
<item>- or !! -- refers to the file you've last visited
<item>˜ -- refers to your home directory
<item>= or + -- refers to your <ref id="folder" name="$folder"> directory