[ttml2] Two value percentage fontSize not fully defined

nigelmegitt has just created a new issue for 
https://github.com/w3c/ttml2:

== Two value percentage fontSize not fully defined ==
If a two value percentage based `tts:fontSize` is used and an ancestor
 element specifies a single value absolute size, the horizontal 
component is undefined. For example:

```xml
<div tts:fontSize="1c">
   <p tts:fontSize="100% 100%">...</p>
</div>
```

In this case the `div` sets a font size defined by height alone, so 
width is undefined. Then the first (horizontal) 100% value in the `p` 
element's `tts:fontSize` attribute is 100% of an unknown value. This 
cannot meaningfully be transformed by a transformation processor.

Solution proposals:

1. Prohibit two value percentage based sizes (simplest solution)
2. Prohibit two value percentage based sizes when the parent element's
 font size has a single value (harder to verify)
3. Define the applicable size to use when calculating the horizontal 
component of a two value percentage based font size if the parent 
element font size has a single value. (most complicated solution)

I would prefer the first of these on first look.

Please view or discuss this issue at 
https://github.com/w3c/ttml2/issues/200 using your GitHub account

Received on Friday, 14 October 2016 15:49:06 UTC