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on 

        # OptionParser.on

(from ruby core)
---
    on(*params, &block)

---

Creates an option from the given parameters `params`. See [Parameters
for New Options](./option_params.rdoc).

The block, if given, is the handler for the created option. When the
option is encountered during command-line parsing, the block is called
with the argument given for the option, if any. See [Option
Handlers](./option_params.rdoc#label-Option+Handlers).

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