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Wide Review Comment 2017: Use of lines as positioning constructs #378
Description
Copy/paste from https://lists.w3.org/Archives/Public/public-tt/2017Sep/0080.html - raising as an issue for tracking/disposition purposes.
It is not clear how the use of lines as a positioning construct is defined. Whereas section 4.4 "line cue setting" says that the height of a line is based on the first line, in §6.1, step 12.1 bullet two, the line height is initialised to a very specific value 5.33vh, regardless of the height of the line, and I can't see anywhere that sets another value in its place (I could not see any reference to the line-height property in the rendering section, but please point me to it if it is there).
#371 is related.
Activity
silviapfeiffer commentedon Oct 28, 2017
The height of the line being calculated based on the first line box is CSS speak for "normal line height above font size", which is typically about 120%. #371 has its own clarification.
§6.1.1 https://www.w3.org/TR/webvtt1/#applying-css-properties specifies that the default font setting is '5vh sans-serif'. So if you read the CSS spec, it implies a line-height of 'normal'. That's how the positioning with lines works.
Is that clarification sufficient?
silviapfeiffer commentedon Nov 11, 2017
TPAC discussion: check if the
lineHeightvariable is getting updated at a later stage in the algorithm with CSS specified in::cuedwsinger commentedon Nov 11, 2017
either clarify in step 12 that the lineHeight can be set by CSS and 5.33vh is the default; or in the CSS section say that when lineHeight changes, the values that depend on lineHeight also have to change
also look for other values that CSS can override, and provide similar text. also try to improve the vague phrase "Apply the terms of the CSS specifications" a few lines later; what does this mean?
dwsinger commentedon Dec 8, 2017
do we need a spec. note clarifying/explaining this?
silviapfeiffer commentedon Dec 8, 2017
Yes, it's still on my todo list