tweak wording a tad

Author: John Daggett

css3-fonts/Fonts.html

@@ -3256,7 +3256,7 @@ <h3 id=font-variant-position-prop><span class=secno>6.4 </span>Subscript,
    subscripts, superscripts and ordinals. These alternate glyphs of reduced
    size are positioned within the same em-box as the default glyph and
    explicitly designed to match the surrounding text and make the them more
-   readable.
+   readable without affecting the linebox.
 
   <div class=figure><img alt="comparison between real subscript glyphs and
    synthesized ones" src=realsubscripts.png>