Can Apps Scripts be used in Gmail to analyze the content of an email as the user is composing it?

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No, Apps Script cannot be used in real-time inside a Gmail compose window to analyze the content of an email as the user is typing it. Apps Script only runs when a trigger is fired or when the user manually runs the script from within the Google Apps Script editor. However, you may create a separate add-on or application that analyzes the content of an email after it has been sent by the user.