Use the passage to answer the question.
But no person who was, on January 1st, 1866, or at any time prior thereto, entitled to vote under any form of government, or who at that time resided in some foreign nation, and no linear descendant of such person, shall be denied the right to register and vote because of his inability to so read and write sections of such Constitution we have difficulty in finding words to more clearly demonstrate the conviction we entertain that the standard has the characteristics which the government attributes to it than does the mere statement of the text. It is true it contains no Express words of an exclusion from the standard which it establishes of any person on account of race, color, or previous condition of servitude prohibited by the 15th amendment, but the standard itself inherently brings that result into existence since it is based purely upon a period of time before the enactment of the 15th amendment and make that period the controlling and dominant test of the right of suffrage.
Which voting practice did the supreme Court decision address?