[css-inline-3] Copy over CSS2.1 10.6.1

Author: frivoal

css-inline-3/Overview.bs

@@ -686,6 +686,36 @@ Inline Box Heights: the 'inline-sizing' property</h3>
 	rename it to match,
 	and possibly introduce any other values that may seem necessary.
 
+<p>The <span class="propinst-height">'height'</span> property does not
+apply. The height of the content area should be based on the font, but
+this specification does not specify how. A UA may, e.g., use the
+em-box or the maximum ascender and descender of the font. (The latter
+would ensure that glyphs with parts above or below the em-box still
+fall within the content area, but leads to differently sized boxes for
+different fonts; the former would ensure authors can control
+background styling relative to the 'line-height', but leads to glyphs
+painting outside their content area.)
+</p>
+<p class=note>Note: level 3 of CSS will probably include a property to
+select which measure of the font is used for the content height.
+</p>
+<p>The vertical padding, border and margin of an inline, non-replaced
+box start at the top and bottom of the content area, and has nothing
+to do with the <span
+class="propinst-line-height">'line-height'</span>. But only the <span
+class="propinst-line-height">'line-height'</span> is used when calculating
+the height of the line box.
+</p>
+<p><a name="multi-font-inline-height"></a> If more than one font is
+used (this could happen when glyphs are found in different fonts), the
+height of the content area is not defined by this specification.
+However, we suggest that the height is chosen such that the content
+area is just high enough for either (1) the em-boxes, or (2) the
+maximum ascenders and descenders, of <em>all</em> the fonts in the
+element. Note that this may be larger than any of the font sizes
+involved, depending on the baseline alignment of the fonts.
+</p>
+
 <h2 id="initial-letter-styling">
 <!--<a name="Initial"></a>-->
 Initial Letters</h2>