Immediately after the follows the default specifier.
This is treated as the contents of a subroutine in the pile's
top package (i.e. global pile variables are available); braces
are optional. Often this is a single constant value or a short
constant list, but more programmatic code can be included.
There are many cases where multiple values are expected;
for more on this, see 8.
As noted in 3.1, this code block will not be executed if MIC believes that there is data present which should override the default data. It is a good idea to make your default data code side- effect free. Return the list of values, but don't go off and execute arbitrary programs or mangle data, etc.
$obj and $index (and all the obj's and indexes of parent groups) will be available in this code block and the arbitrary code block, if they themselves are available. Your code should never depend on any of these, however, as described in 8.2. Note that $fs and $field are not currently made available here.