@rt = (
	q/\b/,	# standard word boundary
	q/(?:(?=\w)(?<!\w)|(?=\W)(?<!\W))/,	# [japhy]-explicit-left
	q/(?:(?<=\w)(?!\w)|(?<=\W)(?!\W))/,	# [japhy]-explicit-right
	q/(?(?=\w)(?<!\w)|(?<!\W))/,	# [japhy]-conditional-left
	q/(?(?<=\w)(?!\w)|(?!\W))/,	# [japhy]-conditional-right
	q/(?:(?=\w)(?<!\w)|(?!\w)(?<=\w))/,	# [ysth]-\b-emulation
);
for my $text ('this,', ',that') {
	for my $rxstr (@rt) {
		my $try = $rxstr . (' ' x (31 - length $rxstr));
		my $rx = qr/$rxstr/;
		(my $txt = $text) =~ s/$rx/*/g;
		print "[$try]$txt\n";
	}
}

##</code><code>##

[\b                             ]*this*,
[(?:(?=\w)(?<!\w)|(?=\W)(?<!\W))]*this*,
[(?:(?<=\w)(?!\w)|(?<=\W)(?!\W))]this*,*
[(?(?=\w)(?<!\w)|(?<!\W))       ]*this*,
[(?(?<=\w)(?!\w)|(?!\W))        ]*this*,*
[(?:(?=\w)(?<!\w)|(?!\w)(?<=\w))]*this*,
[\b                             ],*that*
[(?:(?=\w)(?<!\w)|(?=\W)(?<!\W))]*,*that
[(?:(?<=\w)(?!\w)|(?<=\W)(?!\W))],*that*
[(?(?=\w)(?<!\w)|(?<!\W))       ]*,*that*
[(?(?<=\w)(?!\w)|(?!\W))        ],*that*
[(?:(?=\w)(?<!\w)|(?!\w)(?<=\w))],*that*