I noticed this in a few blocks and wondered what it’s for
It means that the label is translatable.
If I make a dropdown with two options:
$_set x to _
set y to _
and then set the language to another one, the top one will be translated into whatever language I chose, but the bottom one stays verbatim.
The same should work for variadic block labels!
Ta- that explains why removing it made no difference in my experiments :-)
Assuming, of course, that said string has a translation in the Snap files.