[css-fonts-3] Export 'first available font'.

Author: tabatkins

css-fonts-3/Fonts.html

@@ -3369,7 +3369,7 @@ <h3 id=font-style-matching><span class=secno>5.2. </span>Matching font
    consistent as possible across user agents, given an identical set of
    available fonts and rendering technology.
 
-  <p>The <dfn id=first-available-font>first available font</dfn>, used for
+  <p>The <dfn id=first-available-font data-export>first available font</dfn>, used for
    example in the definition of <a
    href="https://www.w3.org/TR/css3-values/#font-relative-lengths"><em>font-relative
    lengths</em></a> such as ‘<code class=property>ex</code>’ and ‘<code

css-fonts-3/Fonts.src.html

@@ -2534,7 +2534,7 @@ <h3 id="font-style-matching">Matching font styles</h3>
 as consistent as possible across user agents, given an identical set
 of available fonts and rendering technology.</p>
 
-<p>The <dfn>first available font</dfn>,
+<p>The <dfn data-export>first available font</dfn>,
 used for example in the definition of <a href="https://www.w3.org/TR/css3-values/#font-relative-lengths"><em>font-relative lengths</em></a>
 such as 'ex' and 'ch'
 or in the definition of the <a href="https://www.w3.org/TR/CSS2/visudet.html#propdef-line-height">'line-height'</a> property,