[csswg-drafts] [css-ruby-1] Default ruby centring for more than just zh

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

== [css-ruby-1] Default ruby centring for more than just zh ==
A.1 Supporting Ruby Layout
https://drafts.csswg.org/css-ruby-1/#default-ua-ruby

the default UA style sheet information includes the following:

```
rtc:lang(zh), rt:lang(zh) {
  ruby-align: center; }
```

This establishes centred display for ruby for Chinese, but there are 
other language subtags that indicate that text is chinese besides the 
generic `zh`.  These should presumably also be included here.  

The current list of more specific tags recommended by the IANA subtag 
registry rather than `zh` is:
`cdo cjy cmn cpx czh czo gan hak hsn lzh mnp nan wuu yue`. 

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/779 using your GitHub 
account