Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

Wikipedia says: A postscript may be a sentence, a paragraph, or occasionally many paragraphs added to, often hastily and incidentally, after the signature of a letter or (sometimes) the main body of an essay or book. When all letters were handwritten, and adding a new thought to the letter would have likely involved rewriting the entire letter, a postscript had obvious practicality. Now, however, one can just as easily add the thought to the main text.
I use a P.S. rather often in my emails, when the content of the P.S. is unrelated to the rest of the body of the message. For example, if I was writing two or three paragraphs about a database problem to a colleague, but I knew his wife had been recently released from the hospital, I might end the message with something like: P.S. I hope your wife is doing better. That's an easy way to make an abrupt transition to something unrelated to the rest of the message. Such modern usage isn't driven by an inability to conveniently insert the text (which is easily done electronically) it's more a matter of how much that closing thought is related to the rest of the message. P.S. You know you can't believe everything you read on Wikipedia, right?