Add issue about whether we want 1em height or ideographic height

Author: fantasai

css3-writing-modes/Overview.html

@@ -2896,6 +2896,10 @@ <h2 id=text-combine><span class=secno>9. </span> Glyph Composition: the
    chosen such that the square is centered between the content edges of its
    parent inline box prior to any baseline alignment shift.
 
+  <p class=issue>Should this use a 1em height, or the height of 水? I.e. is
+   the goal to fit in 1em height, or to fit in the height of an ideographic
+   character?
+
   <p>Any CSS fullwidth transformations (&lsquo;<code
    class=css>text-transform: full-width</code>&rsquo; <a href="#CSS3TEXT"
    rel=biblioentry>[CSS3TEXT]<!--{{CSS3TEXT}}--></a> or &lsquo;<code

css3-writing-modes/Overview.src.html

@@ -2169,6 +2169,10 @@ <h2 id="text-combine">
     square is centered between the content edges of its parent inline
     box prior to any baseline alignment shift.
 
+  <p class="issue">Should this use a 1em height, or the height of 水?
+    I.e. is the goal to fit in 1em height, or to fit in the height of
+    an ideographic character?
+
   <p>Any CSS fullwidth transformations
     (''text-transform: full-width'' [[CSS3TEXT]] or
     ''font-variant-east-asian-width: full-width'' [[CSS3FONT]])