[ttml2] elaborate handling of potentially line area overflowing text combination
--- a/ttml2/spec/ttml2.xml Wed Jan 21 22:05:22 2015 -0800
+++ b/ttml2/spec/ttml2.xml Sun Jan 25 13:58:02 2015 -0700
@@ -10744,16 +10744,18 @@
§ 7.16.9.</p>
</note>
</div3>
-
<div3 id="style-attribute-textCombine">
<head>tts:textCombine</head>
<p>When a vertical writing mode applies, the <att>tts:textCombine</att> attribute is used to specify a style property that
determines whether and how multiple nominally non-combining characters are combined so that their glyph areas
-consume the nominal bounding box of a single em square. If a horizontal writing mode applies, then this property is ignored
+consume the nominal bounding box of a single em square of the surrounding vertical text.
+If a horizontal writing mode applies, then this property is ignored
for the purpose of presentation processing.</p>
-<p>Combination processing may make use of one or more techniques to obtain the goal of visual combination into an em square. For
-example, half-width variant forms may be selected, a ligature may be selected, a smaller font size may be applied, etc. At a minimum, an
-implementation that supports this style property must be able to select half-width variant forms if available.</p>
+<p>Combination processing may make use of one or more techniques to obtain the goal of visual combination into an em square of the surrounding vertical text.
+For example, half-width variant forms may be selected, a ligature may be selected, a smaller font size may be applied, etc. At a minimum, an
+implementation that supports this style property must be able to select half-width variant forms if available. If none of these techniques are
+able to achieve the target dimension along the block progression dimension of the containing line area, then this dimension of the containing line area may be increased if
+permitted by the line stacking strategy in effect.</p>
<p>This attribute may be specified by any
element type
that permits use of attributes in the TT Style Namespace; however, this attribute applies
@@ -10813,7 +10815,6 @@
that defined by <bibref ref="css3-wm"/>, § 9.1.</p>
</note>
</div3>
-
<div3 id="style-attribute-textDecoration">
<head>tts:textDecoration</head>
<p>The <att>tts:textDecoration</att> attribute is used to specify a style property that