Add issue about minimum required range for dimensions.

Author: tabatkins

css3-values/Overview.html

@@ -775,6 +775,9 @@ <h2 id=lengths><span class=secno>5. </span> Distance Units: the &lsquo;<a
    <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> Like
    keywords, unit identifiers are case-insensitive within the ASCII range.
 
+  <p class=issue>We need a minimum required range/precision for dimensions as
+   well. What should it be?
+
   <p>Properties may restrict the length value to some range. If the value is
    outside the allowed range, the declaration is invalid and must be <a
    href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.

css3-values/Overview.src.html

@@ -479,6 +479,8 @@ <h2 id="lengths">
 	[[!CSS21]] Like keywords, unit identifiers are case-insensitive within
 	the ASCII range.
 
+	<p class='issue'>We need a minimum required range/precision for dimensions as well.  What should it be?</p>
+
 	<p>Properties may restrict the length value to some range.
 	If the value is outside the allowed range, the declaration is invalid
 	and must be <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.