[css-values-4] Define computed form of various value types.

(Lost set of changes floating in my repo from 26 Sept 2018,
probably from co-editing session with Birtles.)

Author: fantasai

css-values-4/Overview.bs

@@ -1041,7 +1041,11 @@ Integers: the <<integer>> type</h3>
 	</wpt>
 
 <h4 id="combine-integers">
-Combination of <<integer>></h4>
+Computation and Combination of <<integer>></h4>
+
+	Unless otherwise specified,
+	the <a>computed value</a> of a specified <<integer>>
+	is the specified abstract integer.
 
 	<a>Interpolation</a> of <<integer>> is defined as
 	<var>V</var><sub>result</sub> =
@@ -1101,7 +1105,11 @@ Real Numbers: the <<number>> type</h3>
 	only literal <<number-token>>s do.
 
 <h4 id="combine-numbers">
-Combination of <<number>></h4>
+Computation and Combination of <<number>></h4>
+
+	Unless otherwise specified,
+	the <a>computed value</a> of a specified <<number>>
+	is the specified abstract number.
 
 	<a>Interpolation</a> of <<number>> is defined as
 	<var>V</var><sub>result</sub> =
@@ -1214,7 +1222,12 @@ Percentages: the <<percentage>> type</h3>
 	</wpt>
 
 <h4 id="combine-percentages">
-Combination of <<percentage>></h4>
+Computation and Combination of <<percentage>></h4>
+
+	Unless otherwise specified
+	(such as in 'font-size', which computes its <<percentage>> values to <<length>>),
+	the <a>computed value</a> of a percentage
+	is the specified percentage.
 
 	<a>Interpolation</a> of <<percentage>> is defined as
 	<var>V</var><sub>result</sub> =
@@ -1423,7 +1436,15 @@ Distance Units: the <<length>> type</h2>
 	In cases where the <a lt="used value">used</a> length cannot be supported,
 	user agents must approximate it in the <a lt="actual value">actual</a> value.
 
-	There are two types of length units: <a lt="relative length">relative</a> and <a lt="absolute length">absolute</a>.
+	There are two types of length units:
+	<a lt="relative length unit">relative</a> and <a lt="absolute length unit">absolute</a>.
+	The <a>specified value</a> of a length is
+	represented by its quantity and its unit.
+	The <a>computed value</a> of a length is
+	the specified length resolved to an <a>absolute length</a>,
+	and its unit is not distinguished:
+	it can be represented by any <a>absolute length unit</a>
+	(but will be serialized using its <a>canonical unit</a>, ''px'').
 
 	<wpt>
 	css/css-values/calc-unit-analysis.html
@@ -1438,7 +1459,8 @@ Distance Units: the <<length>> type</h2>
 <h3 id="relative-lengths">
 Relative Lengths</h3>
 
-	<dfn lt="relative length">Relative length units</dfn> specify a length relative to another length.
+	<dfn lt="relative length | relative length unit">Relative length units</dfn>
+	specify a length relative to another length.
 	Style sheets that use relative units can more easily scale from one output environment to another.
 
 	The relative units are:
@@ -2021,7 +2043,8 @@ The Various Viewport-relative Units</h5>
 <h3 id="absolute-lengths">
 Absolute Lengths: the ''cm'', ''mm'', ''Q'', ''in'', ''pt'', ''pc'', ''px'' units</h3>
 
-	The <dfn lt="absolute length">absolute length units</dfn> are fixed in relation to each other
+	The <dfn lt="absolute length | absolute length unit">absolute length units</dfn>
+	are fixed in relation to each other
 	and [=anchored=] to some physical measurement.
 	They are mainly useful when the output environment is known.
 	The absolute units consist of