Absolute & relative coloring. Absolute coloring is what you see by default. Relative coloring: if you click on a country in the table below the years chart, the country will be selected. The color of other country cells will be green, if the value of the cell is less then the value of the selected country for that specific year, or red (a gradient of yellow-red) if a given country has more documents then the selected country. (it's described in the
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