[webvtt] Clarify DOM conversion of timestamp

zcorpan has just created a new issue for https://github.com/w3c/webvtt:

== Clarify DOM conversion of timestamp ==
http://w3c.github.io/webvtt/#ref-for-webvtt-timestamp-object-3

> WebVTT Timestamp Object ProcessingInstruction node whose target is "timestamp" and whose data is a WebVTT timestamp representing the value of the WebVTT Timestamp Object, with all optional components included, with one leading zero if the hours component is less than ten, and with no leading zeros otherwise\.

There is no algorithm for serializing the value (seconds).

http://zcorpan.github.io/live-webvtt-viewer/#vtt=WEBVTT%0A%0A00%3A00%3A00.000+--%3E+00%3A00%3A10.000%0AHello+world.%3C0%3A00%3A05.000%3E

Firefox Nightly 
```
    "html": "Hello world.<?timestamp 00:00:05.000>"
```
Safari TP/Chrome canary
```
    "html": "Hello world.<?timestamp 0:00:05.000?>"
```
(seemingly preserving input, note only one zero in hours)

Please view or discuss this issue at https://github.com/w3c/webvtt/issues/345 using your GitHub account

Received on Tuesday, 18 April 2017 08:53:11 UTC