$_ defaults to OUTER::<$_>

no reason to hide this fact

doc/Type/Block.pod6

@@ -10,11 +10,13 @@ A C<Block> is a code object meant for small-scale code reuse.  A block is
 created syntactically by a list of statements enclosed in curly braces.
 
 Without an explicit signature or placeholder arguments, a block has C<$_>
-as a positional argument
+as a positional argument. Which defaults to the outer scope's $_. Thus it
+will inherit the L<topic|/language/variables#index-entry-topic_variable> if possible.
 
     my $block = { uc $_; };
     say $block.^name;           # OUTPUT: «Block␤»
     say $block('hello');        # OUTPUT: «HELLO␤»
+    say {;}.signature;          # OUTPUT: «(;; $_? is raw = OUTER::<$_>)␤»
 
 A block can have a L<Signature|/type/Signature> between C<< -> >> or C<< <-> >>
 and the block: