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swapcase! 

        # String.swapcase!

(from ruby core)
---
    swapcase!(*options) -> self or nil

---

Upcases each lowercase character in `self`; downcases uppercase
character; returns `self` if any changes were made, `nil` otherwise:

    s = 'Hello World!' # => "Hello World!"
    s.swapcase!        # => "hELLO wORLD!"
    s                  # => "Hello World!"
    ''.swapcase!       # => nil

The casing may be affected by the given `options`; see [Case
Mapping](doc/case_mapping_rdoc.html).

Related: String#swapcase.

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