Resolve w3c#2186: keep 4x4 matrices here, but remove any mention of 3d transform functions from transforms-1, and duplicate the "Transform function primitives and derivatives" section into transforms-2 for the 3D functions. Improve the wording a little.

Author: smfr

css-transforms-1/Overview.bs

@@ -145,8 +145,6 @@ When used in this specification, terms have the meanings assigned in this sectio
 : <dfn>2D matrix</dfn>
 ::  A 3x2 transformation matrix with 6 items or a 4x4 matrix with 16 items, where the items m<sub>31</sub>, m<sub>32</sub>, m<sub>13</sub>, m<sub>23</sub>, m<sub>43</sub>, m<sub>14</sub>, m<sub>24</sub>, m<sub>34</sub> are equal to ''0'' and m<sub>33</sub>, m<sub>44</sub> are equal to ''1''.
 
-	Issue(w3c/csswg-drafts#2186): should this spec mention 4x4 matrices?
-
 : <dfn>identity transform function</dfn>
 :: A <a href="#transform-functions">transform function</a> that is equivalent to a identity 4x4 matrix (see <a href="#mathematical-description">Mathematical Description of Transform Functions</a>). Examples for identity transform functions are ''translate(0)'', ''translateX(0)'', ''translateY(0)'', ''scale(1)'', ''scaleX(1)'', ''scaleY(1)'', ''rotate(0)'', ''skew(0, 0)'', ''skewX(0)'', ''skewY(0)'' and ''matrix(1, 0, 0, 1, 0, 0)''.
 
@@ -274,18 +272,10 @@ Serialization of the computed value of <<transform-list>> {#serialization-of-the
 
 A <<transform-list>> for the computed value is serialized to one <<matrix()>> function by the following algorithm:
 
-Issue(w3c/csswg-drafts#2186): keep 4x4 matrix here and below?
-
 <ol class="algorithm">
 	1. Let <var>transform</var> be a 4x4 matrix initialized to the identity matrix. The elements <var ignore> m11</var>, <var ignore>m22</var>, <var ignore>m33</var> and <var ignore>m44</var> of <var>transform</var> must be set to ''1'' all other elements of <var>transform</var> must be set to ''0''.
 	2. Post-multiply all <<transform-function>>s in <<transform-list>> to <var>transform</var>.
-	3. Chose between <<matrix()>> or <<matrix3d()>> serialization:
-		<dl class="switch">
-		  <dt>If <var>transform</var> is a [=2D matrix=]
-		  <dd>Serialize <var>transform</var> to a <<matrix()>> function.
-		  <dt>Otherwise
-		  <dd>Serialize <var>transform</var> to a <<matrix3d()>> function.
-		</dl>
+	3. Serialize <var>transform</var> to a <<matrix()>> function.
 </ol>
 
 The 'transform-origin' Property {#transform-origin-property}
@@ -668,6 +658,24 @@ A percentage for vertical translations is relative to the height of the [=refere
 </dl>
 
 
+Transform function primitives and derivatives {#transform-primitives}
+---------------------------------------------
+
+Some transform functions can be represented by more generic transform functions. These transform functions are called derived transform functions, and the generic transform functions are called primitive transform functions. Two-dimensional primitives and their derived transform functions are:
+
+<dl>
+	<dt id="translate-primitive">''translate()''
+	<dd>for <<translateX()>>, <<translateY()>> and <<translate()>>.
+
+	<dt id="rotate-three-primitive">''rotate()'' with three arguments
+	<dd>for <<rotate()>> with one or three arguments if <a href="#svg-transform-functions">rotate with three arguments</a> is supported.
+
+	<dt id="scale-primitive">''scale()''
+	<dd>for <<scaleX()>>, <<scaleY()>> and <<scale()>>.
+
+</dl>
+
+
 The Transform Function Lists {#transform-function-lists}
 ========================================================
 
@@ -752,43 +760,6 @@ In some cases, an animation might cause a transformation matrix to be singular o
 
 Issue(w3c/csswg-drafts#927): Use proposed tranform interpolation from GitHub issue.
 
-Transform function primitives and derivatives {#transform-primitives}
-=====================================================================
-
-Some transform functions can be represented by more generic transform functions. These transform functions are called derived transform functions, the generic transform functions primitives. Primitives for two-dimensional and three-dimensional transform functions are listed below.
-
-Two-dimensional primitives with derived transform functions are:
-
-<dl>
-	<dt id="translate-primitive">''translate()''
-	<dd>for <<translateX()>>, <<translateY()>> and <<translate()>>.
-
-	<dt id="rotate-three-primitive">''rotate()'' with three arguments
-	<dd>for <<rotate()>> with one or three arguments if <a href="#svg-transform-functions">rotate with three arguments</a> is supported.
-
-	<dt id="scale-primitive">''scale()''
-	<dd>for <<scaleX()>>, <<scaleY()>> and <<scale()>>.
-
-</dl>
-
-Issue(w3c/csswg-drafts#2186): Move the following lines to CSS-Transforms-2.
-
-Three-dimensional primitives with derived transform functions are:
-
-<dl>
-	<dt id="translate3d-primitive">''translate3d()''
-	<dd>for <<translateX()>>, <<translateY()>>, ''translateZ()'' and <<translate()>>.
-
-	<dt id="scale3d-primitive">''scale3d()''
-	<dd>for <<scaleX()>>, <<scaleY()>>, ''scaleZ()'' and <<scale()>>.
-
-	<dt id="rotate3d-primitive">''rotate3d()''
-	<dd>for <<rotate()>>, ''rotateX()'', ''rotateY()'' and ''rotateZ()''.
-</dl>
-
-<p id="interpolation-two-three-dimensional-function">
-  For derived transform functions that have a two-dimensional primitive and a three-dimensional primitive, the context decides about the used primitive. See <a href="#interpolation-of-transform-functions">Interpolation of primitives and derived transform functions</a>.
-
 
 Interpolation of primitives and derived transform functions {#interpolation-of-transform-functions}
 ===================================================================================================

css-transforms-2/Overview.bs

@@ -851,6 +851,26 @@ In the following <dfn export>3d transform functions</dfn>, a <<zero>> behaves th
 :: specifies a <a href="#PerspectiveDefined">perspective projection matrix</a>. This matrix scales points in X and Y based on their Z value, scaling points with positive Z values away from the origin, and those with negative Z values towards the origin. Points on the z=0 plane are unchanged. The parameter represents the distance of the z=0 plane from the viewer. Lower values give a more flattened pyramid and therefore a more pronounced perspective effect. For example, a value of 1000px gives a moderate amount of foreshortening and a value of 200px gives an extreme amount. The value for depth must be greater than zero, otherwise the function is invalid.
 
 
+Transform function primitives and derivatives {#transform-primitives}
+----------------------------
+
+Some transform functions can be represented by more generic transform functions. These transform functions are called derived transform functions, and the generic transform functions are called primitive transform functions. Three-dimensional primitives and their derived transform functions are:
+
+<dl>
+	<dt id="translate3d-primitive">''translate3d()''
+	<dd>for <<translateX()>>, <<translateY()>>, ''translateZ()'' and <<translate()>>.
+
+	<dt id="scale3d-primitive">''scale3d()''
+	<dd>for <<scaleX()>>, <<scaleY()>>, ''scaleZ()'' and <<scale()>>.
+
+	<dt id="rotate3d-primitive">''rotate3d()''
+	<dd>for <<rotate()>>, ''rotateX()'', ''rotateY()'' and ''rotateZ()''.
+</dl>
+
+<p id="interpolation-two-three-dimensional-function">
+  For derived transform functions that have a two-dimensional primitive and a three-dimensional primitive, the context decides about the used primitive. See <a href="#interpolation-of-transform-functions">Interpolation of primitives and derived transform functions</a>.
+
+
 Interpolation of 3D matrices {#interpolation-of-3d-matrices}
 ----------------------------