Curly brackets are a shortcut for <<print $var>> = {var} or {$var}

These are also equivalent:
<<print $obj.leaf>> = {$obj.leaf} or {$obj leaf} or {obj.leaf}

This also equivalent if there is no TwineQuest label for obj
{obj leaf}

NOTE1: $prefix forces TwineQuest to use Twine variable (which TwineQuest
objects usually are too)
NOTE2: either a {dot.syntax} or {space syntax} are just fine
NOTE4: text is output into a span with the class "tq_print_var"
NOTE3: the Twine variable store can be traversed to arbitrary depths:
{$mob.body.leg.foot.toe.toenail} will work as expected you can even try:
{$mob body leg foot toe toenail}