Brackets.
Brackets indicate that the included matter is inserted by another person than the original author; that is, by a person who is quoting or editing the passage. Thus: “He [Goethe] tells us that character is developed in the busy world, though intellect is developed in solitude.”
The Exclamation Point.
1. There is a tendency to punctuate with the period sentences that are really exclamatory; it is better to use the exclamation point. Thus: “I am so delighted to see you!”
It is better still to avoid an excess of exclamatory sentences, however correctly punctuated.
2. The word oh! should be followed by an exclamation point or by a comma. This is not the word O, which is used in direct address—
“O thou that rollest above,
Round as the shield of my fathers,”
and to express a wish:
“O that I had wings like a dove.”