Yes, you are right it's not in the manual yet. The reason was that I hoped to come up with a better mapping than it is now (and didn't think it would take that long

). I'm going to update the manual with the description of the current keymap regardless now.
As quick information for you beforehand: "Rec + Left/Right" moves the cursor, "Rec + Down" to delete a character, "Power" leaves the virtual keyboard without saving the changes, "Vol Up" or "Vol Down" both accept the changes and take you back to the main menu.