[css-properties-values-api] Canonical units for computed values, etc. (#831)

Resolves issue #826.

Author: andruud

css-properties-values-api/Overview.bs

@@ -405,9 +405,14 @@ For <length-percentage> values, the computed value is one of the following:
 *   otherwise, the computed value is a calc expression containing an absolute
 	length expressed in pixels, and a percentage value.
 
-For <custom-ident>, ident, <color>, <integer>,
-<angle>, <time>, <resolution> or "*" values, the
-computed value is as specified.
+For <color> values, the value is computed as described in
+	[[css-color-4#resolving-color-values]].
+
+For <angle>, <time> and <resolution> values, the computed value is the
+value expressed in its [=canonical unit=], with ''calc()'' expressions
+evaluated [[css-values-4#calc-computed-value|as described in CSS Values]].
+
+For <custom-ident>, ident, or "*" values, the computed value is as specified.
 
 For <url> values, the computed value is one of the following:
 
@@ -419,10 +424,12 @@ For <image> values, the computed value is as specified, except that relative
 URLs that appear in the value are resolved to absolute URLs as described in
 [[!css3-values]], and all lengths are resolved to their computed values.
 
-For <number> and <percentage> values which are not calc expressions, the
-computed value is as specified. Calc expressions that are
-<number> and <percentage> values get reduced during computation to simple
-numbers and percentages respectively.
+For <integer>, <number> and <percentage> values, the computed value is
+one of the following:
+
+* if the specified value is a ''calc()'' expression, the computed value is the
+	evaluated result of that expression.
+* otherwise, the computed value is as specified.
 
 For <transform-function> values (including those contained in <transform-list> values),
 the computed value is as specified but with all lengths resolved to their