[i18n-activity] Default directions in mixed textOrientation should use TR50

r12a has just created a new issue for https://github.com/w3c/i18n-activity:

== Default directions in mixed textOrientation should use TR50 ==
10.2.46 tts:textOrientation
http://w3c.github.io/ttml2/spec/ttml2.html#style-attribute-textOrientation

> If the value of this attribute is mixed, then, in vertical writing modes, glyphs from horizontal scripts are set sideways, i.e., 90° clockwise from their nominal orientation in horizontal text, while glyphs from vertical scripts are not affected.

The terms 'vertical scripts' and 'horizontal scripts' don't appear to have any definition.

I think this paragraph should actually say that the defaults specified in http://www.unicode.org/reports/tr50/ should be applied for mixed text.

Please view or discuss this issue at https://github.com/w3c/i18n-activity/issues/357 using your GitHub account