How does "Modify" Work?

[ContrabassDrio]

How does the "Modify" tool work? I know Badspot and the moderators have it all the time, but how does it sometimes appear and sometimes not?

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[GenaralSkar]

It's not in help because some people were deleting OP when they got the problem fixed and it's not in drama so people don't edit their posts to make them seem like not as much of an idiot or bad guy.