regions, id
<link rel="help" href="https://w3c.github.io/webvtt/#collect-webvtt-region-settings">

assert_equals(cues.length, 4);

var region1 = cues[0].region;
assert_equals(region1.lines, 2);

var region2 = cues[1].region;
assert_equals(region2.lines, 1);

var region3 = cues[2].region;
assert_equals(region3.lines, 3);

var region4 = cues[3].region;
assert_equals(region4.lines, 4);

===
WEBVTT

NOTE No API for accessing region ids, so using lines to uniquely identify regions

REGION
id:foo
id:bar
lines:1

REGION
id:bar id:foo
lines:2

REGION
id:id
id: foo
id :bar
lines:3

REGION
id:\v
lines:4

00:00:00.000 --> 00:00:01.000 region:foo
valid

00:00:00.000 --> 00:00:01.000 region:bar
valid

00:00:00.000 --> 00:00:01.000 region:id
valid

00:00:00.000 --> 00:00:01.000 region:\v
valid