Regarding initial value of tts:lineHeight

[plehegar]

TTML1SE added a non-normative recommendation for lineHeight: 8.2.12: "Note: It is recommended that presentation processors use a computed line height that is 125% of the size of the largest applicable font size when the value normal is specified. The choice of 125% allows use of a font size of 0.8c in order to obtain a line height of 1c."

However, the WG had previously agreed to 120% which was codified in an editor's draft after closing ISSUE-275. The issue includes the rationale. The Note was a last minute change for the reason stated in the last sentence in the note.

Implementations had been developed to roughly 120% which was re-enforced by the editor's draft text.

This recommendation should be revisited and normative provisions added to TTML2.

Detailed background information can be found here: http://lists.w3.org/Archives/Public/public-tt/2013Aug/0057.html

This is also related to ISSUE-283 and ISSUE-302.

(raised by Mike Dolan on 2013-10-11)
From tracker issue http://www.w3.org/AudioVideo/TT/tracker/issues/284

[nigelmegitt]

Note that ISSUE-283 was moved to #86 and ISSUE-302 to #101 here.

Also, for CSS in general the equivalent to tts:lineHeight="normal" would be line-height: normal; for which implementations offer varying default equivalent percentages, which in any case are only fallbacks in case the data in the font cannot provide a calculated value.

I'm not clear what normative provisions yoyu wanted to add to TTML2 @mikedo ? Some work has been done on tts:lineHeight to define the algorithm when the value is "normal" and this remains work in progress I think.

[skynavga]

Marking as works for me and closing. If @mikedo still thinks this needs revisiting, then please reopen and add discussion needed label.