The fact that I can write some_option => 1, as :some_option makes me very happy. Turning something on or off is, often, over half the parameters passed to some function or constructor.

I should also point out that this was intentionally modelled both on the Unix command line's use of '-' (without the negative connotations of '-'), as well as the existing option syntax for I/O layers in Perl 5, which we've generalized from working only inside the mode string to working in any argument list. We can also probably extend it to work as an adverbial syntax on operators:

$a .. $b :by(3)
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And it still just comes in as an optional parameter, just as if you'd said:

infix:..($a, $b, by => 3)
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In a sense, the colon marker on the front serves a similar function to the -ly suffix in English, or the -ku/-ni suffixes in Japanese.