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I am assuming that ellipsis must be followed by exclamation mark like this:
If only Mark (had) understood this matter . . . !

Is this right? Also, must (had) be included?
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An ellipse is three dots with no spaces. The exclamation point seems incompatible with the ellipsis (a sudden ejaculation vs a tapering off), and I would choose one or the other.

If only Mark understood and if only Mark had understood have different meanings.
Without the exclamation mark, must we add a period to end this sentence? We'll get four dots, then. I am assuming that isn't necessary because it isn't a complete sentence.
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First I have to go back and correct myself: evidently, some style manuals say ellipses have spaces between the dots. So I think it rests with your teacher or editor to choose.

You would need to use that fourth dot if the matrix sentence finished at the ellipsis, but if it is dialog, then just the three spaced dots of 'faltering speech', it is called.
Thank you for your patience, Mr. M. My doubt is whether 'if only' statements (such as the example I gave) are considered complete sentences, in which case a period would be absolutely essential. If not, I'll have no choice but to put an ellipsis (because some sort of punctuation would be needed, anyway).
Ah! I see. In dialog it would be considered a complete utterance:

If only Mark (had) understood this matter!
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Look all i wanted was an answer and everyone has commented on it. i need this for my homework! it has to be due in soon and i don't know? please tell me thanks? yes or a no? thanks
Anonymousyes or a no? thanks
No.

Without getting technical, the answer, as my 7 year old son sees it, is that it depends on what you are trying to express.

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