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downcase! 

        # String.downcase!

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

---

Downcases the characters in `self`; returns `self` if any changes were
made, `nil` otherwise:

    s = 'Hello World!' # => "Hello World!"
    s.downcase!        # => "hello world!"
    s                  # => "hello world!"
    s.downcase!        # => nil

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

Related: String#downcase, String#upcase, String#upcase!.

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