Add font selection caveat, don't reference hanging glyphs

Author: szager-chromium

css-text-3/Overview.bs

@@ -8262,38 +8262,44 @@ Ink Overflow from Text</h2>
         <p><em>This appendix is non-normative.</em></p>
 
 	<div class="example">
-	  <p>The example below demonstrates a [=hanging glyph=].</p>
+	  <p>The example below demonstrates [=ink overflow=] from text.</p>
 	  <div class="figure" style="margin:0; font-size:10rem; font-family:garamond; font-style:italic">
 	    <span style="display:inline-block; width:1ch; height:1lh; background:green; opacity:0.5"></span><span style="vertical-align: top;">f</span><span style="display:inline-block; width:1ch; height:1lh; background:green; opacity:0.5"></span>
 	  </div>
 	</div>
 
-	Because [=hanging glyphs=] are considered [=ink overflow=],
-	and hence are not included in [=inline box=] geometry,
-	there is no straightforward way to measure their extent,
+	Some glyphs have a painted area that extends beyond the
+	bounding box described by their origin and advance.
+	In these cases, the extra painted area generates [=ink overflow=],
+	and hence is not included in [=inline box=] geometry.
+	There is no straightforward way to measure the extent
+	of [=ink overflow=] generated by these glyphs,
 	or to pre-compute padding or margin lengths that will
-	prevent [=hanging glyphs=] from overlapping adjacent content.
-	The extent of [=ink overflow=] from [=hanging glyphs=]
-	is determined by the font rendering system,
-	and beyond the scope of this specification.
+	prevent them from overlapping adjacent content.
+	The actual extent of [=ink overflow=] is determined by the font rendering system,
+	and is beyond the scope of this specification.
 
 	However, any two conforming browser implementations,
 	when rendering a given piece of text content
 	using a given font in a supported format
 	(see [[css-fonts-4#font-format-definitions]]),
 	will produce identically-sized [=ink overflow rectangles=],
-	within a 2-pixel margin of error.
-
-	A practical way to prevent [=hanging glyphs=] from
+	within a 2-pixel margin of error. For a known font,
+	a practical way to prevent glyph [=ink overflow=] from
 	overlapping adjacent content is to load the target
 	content in any conforming web browser, gauge the extent
-	of [=ink overflow=] from [=hanging glyphs=] via visual inspection,
+	of [=ink overflow=] via visual inspection,
 	and adjust padding/margin lengths to avoid overlap, plus
 	an extra two pixels to allow for variations between implementations.
-	This should be sufficient to prevent unwanted overlap in all
-	conforming implementations without the necessity of testing
-	each implementation individually.
 
+	Note that there are many factors that may cause the glyph rendering subsystem
+	to use a font other than the one specified in stylesheets when drawing text,
+	including but not limited to UA settings, accessibility features,
+	and the availability of web fonts.
+	The extent of [=ink overflow=] derives from the actual font used for rendering text,
+	and developers should allow for the possibility that
+	the actual rendered extent of [=ink overflow=] from text
+	does not match what they measured during development.
 
 <h2 id="priv" class="no-num">
 Privacy Considerations</h2>