 #   lastRk  : integer, rank of the last  photo of the month
 # }
 #
+#
 # 3/ @nPhotos
 #   Total number of images in the long list.
+#
 #
 # 4/ "rank"
 #   all images are indexed by their rank being their position in the ordered
 #   list of images.
 #   The most recent image rank is 0, the oldest rank is nPhoto - 1
 #
+#
 # 5/ inMonthRank
 #   The rank of the image in the chronological list of images of the same month
 #
-# 6/ buffer
+#
+# 6/ buffer :
+#
+#   The buffer lists all the created thumbs, keep a reference on the first (top
+#   most) and the last (bottom most) cells.
+#   The data structure of the buffer is a closed double linked chain.
+#   Each element of the chain is a "thumb" with a previous (prev) and next
+#   (next) element.
+#   "closed" means that buffer.last.prev == buffer.first
+#
+#   data structure :
 #      first   : {thumb}   # top most thumb
 #      firstRk : {integer} # rank of the first image of the buffer
 #      last    : {thumb}   # bottom most thumb

                label$.dataset.monthRk = rk
                @index$.appendChild(label$)
            ##
            #
            if bufferAlreadyAdapted
                _rePositionThumbs()
            bufferAlreadyAdapted = true


        @_scrollHandler = _scrollHandler

        ###*
         * returns the font-size in px of a given element (context) or of the
         * root element of the document if no context is provided.
         * @param  {element} context Optionnal: an elemment to get the font-size
         * @return {integer}         the font-size
        ###
        getElementFontSize=( context )->
            # Returns a number
            return parseFloat(
