It does, except it doesn't work:

my @a = ("a  sTrinG\n" );
s#(.)(\w+ ?)#\U\1\L\2#g for @a;
print @a;
__END__
a  string
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Two things are happening here: The first is that this requires each word to be two characters or more (so it fails on the initial "a"). The second is that the . can match a space, so " sTrinG" fails because \1 contains a space.

I suggest

s{ \b(\w+) }{\u\L$1}gx;
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