Oops, sorry about that. I'd given the answer in a /msg and totally forgotten that I hadn't given it in a node.

Recall that this is a fairly ambiguous question, and that my answer really just reveals what the source considers to be different scopes.

That answer is found in cop.h, line 360 as of recent perls.

#define CXt_NULL        0
#define CXt_SUB         1
#define CXt_EVAL        2
#define CXt_LOOP        3
#define CXt_SUBST       4
#define CXt_BLOCK       5
#define CXt_FORMAT      6
[download]

OK, the easy ones first

• CXt_LOOP is for, e.g., while (<>) { ... }.
• CXt_BLOCK is for regular old blocks, like do { ... } while <>.
• CXt_EVAL is for eval STRING, not eval BLOCK, which is covered by CXt_BLOCK.
• CXt_SUB is for a subroutine.

That leaves three: CXt_NULL, CXt_SUBST, and CXt_FORMAT. You can probably guess what CXt_SUBST and CXt_FORMAT do, even though the fact that they start new scopes may be surprising.

[~] $ perl -le'$_="foo";s/foo/my $x="bar"/e;print;print ">>>$x<<<"'
bar
>>><<<
[download]

There's s/// creating a new scope. Here's format:

[~] $ cat tmp/format 
format =
@<<<<<<<
my $x = "foo"
.
write;
print ">>>$x<<<";
[~] $ perl -l !$
perl -l tmp/format
foo
>>><<<
[download]

OK, so what does that leave us with? CXt_NULL. CXt_NULL is the block passed to `sort', strangely enough. It's also referred to as a pseudo-block throughout the source.

-dlc