#506 Need for a method to replace a matched character with its inverse casing?

[Kurt De Keyser]

Example of a subtitle-fragment: «to analyze the e.E.G. Signals».
1) «e.E.G.» should become «E.E.G.» (abnormal first lower character in the abbreviation)
2) «Signals» should become «signals» (not a priori a capital after an abbreviation)
So I'd need a method to replace a matched single-character with its uppercase variant if lowercase, and vice versa.
Should also be valid on more exotic characters, such as å versus Å.