I think this is a great question for one of our booktech staff. I'll forward your question over to them.
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You don't have to implement that option, it should already be there.
In TextEdit, with some text selected in a text document, go to the Edit menu and you should see "Transformations" in the lower part of the menu, under Substitutions.
Once you put your cursor over the Transformation menu item, you'll see the submenu options.
I hope that helps,
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