x

Author: howcom

css3-values/Overview.html

@@ -25,13 +25,13 @@
 
    <h1 id=css3-template>CSS3 Values and Units</h1>
 
-   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 9 August 2010</h2>
+   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 10 August 2010</h2>
 
    <dl>
     <dt>This version:
 
     <dd><a
-     href="http://www.w3.org/TR/2010/ED-css3-values-20100809">http://www.w3.org/TR/2010/ED-css3-values-20100809</a>
+     href="http://www.w3.org/TR/2010/ED-css3-values-20100810">http://www.w3.org/TR/2010/ED-css3-values-20100810</a>
 
     <dt>Latest version:
 
@@ -860,57 +860,58 @@ <h4 id=the-calc-min-and-max-functions><span class=secno>6.3.3. </span>The
   <pre>
 S       : calc | min | max;
 calc    : "calc(" S* sum ")" S*;
-min     : "min(" S* sum [ "," S* sum ]* )"" S*;
-max     : "max(" S* sum [ "," S* sum ]* ")" S*;
-sum     : product [ S+ [ "+" | "-" ] S+ product ]*;
-product : unit [[ "*" S* unit ] | [ "/" S* NUMBER ]] *;
-unit    : ["+"|"-"]? [ NUMBER S* | DIMENSION S* | PERCENTAGE S* |
-          min | max | "(" S* sum ")" S* ];
-</pre>
-  <!--
-<pre>
-S       : calc | min | max;
-calc    : "calc(" S* sum ")" S*;
-min     : "min(" S* sum [ "," S* sum ]* )"" S*;
+min     : "min(" S* sum [ "," S* sum ]* ")" S*;
 max     : "max(" S* sum [ "," S* sum ]* ")" S*;
 sum     : product [ [ "+" | "-" ] S* product ]*;
 product : unit [ [ "*" | "/" | "mod" ] S* unit ]*;
 unit    : ["+"|"-"]? [ NUMBER S* | DIMENSION S* | PERCENTAGE S* |
           min | max | "(" S* sum ")" S* ];
 </pre>
--->
 
-  <p>Division by zero is a parse error. <!--
-<p>Values inside a calc() expression must all be either (a)
-numbers or (b) legal values for the property, or values that
-would be legal if it weren't for range restrictions (such
-as the restriction that &lsquo;<code class=property>width</code>&rsquo; accepts only positive values).
--->
-   
-
-  <p>The semantic constraints are as follows: The context of the expression
-   imposes a <em>target type</em>, which is one of length, frequency, angle,
-   time, or number. Any PERCENTAGE token in the expression has the target
-   type. The NUMBER tokens are of type number, and the DIMENSION tokens have
-   types of their units (&lsquo;<code class=property>cm</code>&rsquo; is
-   length, &lsquo;<code class=property>deg</code>&rsquo; is angle etc.). At
-   each operator, the types of the left and right side have to be compared
-   and, if compatible, they yield a <em>result type</em>, roughly as follows
-   (the following ignores precedence rules on the operators for simplicity):
+  <p>The context of the expression imposes a target type, which is one of
+   length, frequency, angle, time, or number. NUMBER tokens are of type
+   number. DIMENSION tokens have types of their units (&lsquo;<code
+   class=property>cm</code>&rsquo; is length, &lsquo;<code
+   class=property>deg</code>&rsquo; is angle etc.); any DIMENSION whose type
+   does not match the target type is not allowed and must be a parse error.
+   If percentages are accepted in that context and convertible to the target
+   type, a PERCENTAGE token in the expression has the target type; otherwise
+   percentages are not allowed and must be a parse error.
+
+  <p>To make expressions simpler, operators have restriction on the types
+   they accept. At each operator, the types of the left and right side have
+   to be checked for these restrictions. If compatible, they return roughly
+   as follows (the following ignores precedence rules on the operators for
+   simplicity):
 
   <ol>
    <li>At ",", "+", "-":<br>
     check: both sides have the same type<br>
     return: that type
 
    <li>At "*":<br>
-    check: at least one side is "number" return: the type of the other side
+    check: at least one side is "number" <br>
+    return: the type of the other side
 
    <li>At "/":<br>
     check: right side is "number"<br>
     return: the type of the left side
   </ol>
 
+  <p>Division by zero is a parse error.
+
+  <p>The value resulting from an expression must be clamped to the range
+   allowed in the target context.
+
+  <div class=example> These two are equivalentequivalent to &lsquo;<code
+   class=css>width: 0px</code>&rsquo; since widths smaller than 0px are not
+   allowed.
+   <pre>
+width: calc(5px - 10px);
+width: 0px;
+</pre>
+  </div>
+
   <p>Given the complexities of &lsquo;<code
    class=property>width</code>&rsquo; and &lsquo;<code
    class=property>height</code>&rsquo; on table cells and table elements,