[css-fonts] Make larger/smaller simple ratios

#1711

Author: Litherum

css-fonts-4/Overview.bs

@@ -636,18 +636,23 @@ Values have the following meanings:
 	<dt><dfn><<relative-size>></dfn>
 	<dd>
 		A <<relative-size>> keyword is interpreted
-		relative to the table of font sizes and the computed 'font-size' of the
-		parent element. Possible values are:
+		relative to the computed 'font-size' of the
+		parent element and possibly the table of font sizes. Possible values are:
 
 		<pre class=prod>[ larger | smaller ]</pre>
 
-		For example, if the parent element has a font size of
-		''medium'', a value of ''larger'' will make the font size of the
-		current element be ''large''.  If the parent element's size is not
-		close to a table entry, the user agent is free to interpolate
-		between table entries or round off to the closest one. The user
-		agent might have to extrapolate table values if the numerical value
-		goes beyond the keywords.
+		If the parent element has a keyword font size in the previous table, ''larger''
+                may make the font size equal to the next entry in the
+                table, and ''smaller'' may make the font size of the current element equal to the previous entry in the table.
+
+                For example, if the parent element has a font size of ''medium'', a value of ''larger'' may make the font size of the current element be ''large''.
+
+                Instead of using next and previous items in the previous keyword table,
+                User Agents may instead use a simple ratio to increase or decrease the
+                font size relative to the parent element. The specific ratio is unspecified,
+                but should be around 1.2 - 1.5. This ratio may vary across different elements.
+
+                Note: A sight-impared user may request a User Agent use a higher ratio than default, in order to aid readability. In addition, a User Agent may choose to use different ratios when it detects paragraph text as opposed to title text.
 
 	<dt><dfn><<length-percentage>></dfn>
 	<dd>