I have just read DeVinne’s “Practice of Typography.”
The same rule applies to the use of the other low marks, comma, semicolon, and colon, in connection with quotation marks. Unlike most rules of grammar and punctuation, this rule does not rest on a logical basis. It rests on purely typographic considerations, as the arrangement of points indicated by the rule gives a better looking line than can be secured by any other arrangement.
Other Uses of the Period
1. The period is used as a decimal point.
2. The period is used in groups, separated by spaces, to indicate an ellipsis.
He read as follows: “The gentleman said . . . .
he was there and saw . . . . the act in question.”