what's the semantics of 'varX is varY', in particular `strX is strY`?

[Adam D. Ruppe]

On Wednesday, 5 August 2020 at 17:29:09 UTC, mw wrote:
> so here `is` means compare strings by their contents?

They both refer to the same string there... the literal gets 
reused by the compiler. Put a .dup on one of the strings and then 
is will not return true anymore.

> where is the exact definition of the  semantics of 'varX is 
> varY'?

It checks if the memory for the variable is the same.