[i18n-activity] Should rubyOverhang:allow overlap ideographs in Japanese?

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

== Should rubyOverhang:allow overlap ideographs in Japanese? ==
10.2.38 tts:rubyOverhangClass
https://www.w3.org/TR/2016/WD-ttml2-20161117/#style-attribute-rubyOverhangClass

My reading of jLReq is that by default it does not allow overlap of 
kanji characters. See the [bullet points just below Fig 
136](https://w3c.github.io/jlreq/#adjustments_of_ruby_with_length_longer_than_that_of_the_base_characters).

> a. Ruby text shall not hang over the ideographic characters (cl-19) 
adjacent to the base characters.

Notes further down admit alternative styles, one of which allows 
overhang of kanji, the other forbids any overhang at all, but these 
seem not to be mainstream.

Therefore, i suspect that 

> If the language of the base text is specified or can be inferred as 
Japanese, then auto should be interpreted as if the following were 
specified: ideographic hiragana punctuationMarks.

should drop the `ideographic`.



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