| TODO. When used as the first dialogue command, stands for "dialogueSingle". Likely a check for whether the player is dating the specified character.
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| Creates a line of dialogue which the character will only see once (at most). {{t|1st-time text}} is shown only if {{t|letter ID}} has not been marked as sent yet (and this marks it as sent); otherwise, {{t|nth-time text}} is shown. {{t|letter ID}} should not correspond to an actual piece of mail (because it will not be sent), but it can be referenced by events or other dialogue lines.