[css-writing-modes] on using the advance height of U+6C34

1. In the last paragraph in Section 9.1.3 it says:

> In some fonts, the ideographic glyphs are given a compressed design such
that they are 1em wide but shorter than 1em tall. To accommodate such
fonts, the UA may vertically scale the the composition to match the advance
height of 水 U+6C34.

However, in the first paragraph in Section 9.1.2 it says:

> The effective size of the composition is assumed to be 1em square

What if the font is an extended font? Will the composition still be 1em
square even if the UA doesn't scale the composition?

2. What happens if the font doesn't have a character for U+6C34.
Furthermore, which font should the UA choose, the first available font?

-- 
Masataka Yakura
<myakura.web@gmail.com>