Illustration of keywords
------------------------

    x - current occurence
    o - selected occurence

    last         _ _ _ o x _ _ _ _
    last+        _ _ _ _ o _ _ _ _
    last++       _ _ _ _ x o _ _ _
    last-        _ _ o _ x _ _ _ _
    last--       _ o _ _ x _ _ _ _
    last+1       _ _ _ _ x o _ _ _
    last+2       _ _ _ _ x _ o _ _
    last-1       _ _ o _ x _ _ _ _
    last-2       _ o _ _ x _ _ _ _

    this         _ _ _ _ o _ _ _ _
    this+        _ _ _ _ x o _ _ _
    this++       _ _ _ _ x _ o _ _
    this-        _ _ _ o x _ _ _ _
    this--       _ _ o _ x _ _ _ _
    this+1       _ _ _ _ x o _ _ _
    this+2       _ _ _ _ x _ o _ _
    this-1       _ _ _ o x _ _ _ _
    this-2       _ _ o _ x _ _ _ _

    next         _ _ _ _ x o _ _ _
    next+        _ _ _ _ x _ o _ _
    next++       _ _ _ _ x _ _ o _
    next-        _ _ _ _ o _ _ _ _
    next--       _ _ _ o x _ _ _ _
    next+1       _ _ _ _ x _ o _ _
    next+2       _ _ _ _ x _ _ o _
    next-1       _ _ _ _ o _ _ _ _
    next-2       _ _ _ o x _ _ _ _