settings, size
<link rel="help" href="https://w3c.github.io/webvtt/#collect-webvtt-cue-timings-and-settings">

assert_equals(cues.length, 16);

var valid_sizes = [
    100,
    2,
    0,
    0,
    100,
    50,
    1.5,
];
valid_sizes.forEach(function(valid, index) {
    assert_equals(cues[index].size, valid, 'Failed with cue ' + index);
});

for (var i = 0; i < 9; i++) {
    var index = valid_sizes.length + i;

    assert_equals(cues[index].size, 100, 'Failed with cue ' + index);
}

===
WEBVTT

NOTE valid

00:00:00.000 --> 00:00:01.000
text0

00:00:00.000 --> 00:00:01.000 size:1xx size:2%
text1

00:00:00.000 --> 00:00:01.000 size:0%
text2

00:00:00.000 --> 00:00:01.000 size:00%
text3

00:00:00.000 --> 00:00:01.000 size:50% size:100%
text4

00:00:00.000 --> 00:00:01.000 size:50% size:101%
text5

00:00:00.000 --> 00:00:01.000 size:1.5%
text6

NOTE invalid

00:00:00.000 --> 00:00:01.000 size:
invalid7

00:00:00.000 --> 00:00:01.000 size:x
invalid8

00:00:00.000 --> 00:00:01.000 size:%
invalid9

00:00:00.000 --> 00:00:01.000 size:%%
invalid10

00:00:00.000 --> 00:00:01.000 size:1%%
invalid11

00:00:00.000 --> 00:00:01.000 size:1%x
invalid12

00:00:00.000 --> 00:00:01.000 size:101%
invalid13

00:00:00.000 --> 00:00:01.000 size:-3%
invalid14

00:00:00.000 --> 00:00:01.000 size:200%
invalid15