[various] Revert generic unitless-0 <angle>, spec <zero> in V&U, make Images and Transforms use it to handle their legacy unitless-0 angles.

Author: tabatkins

css-images/Overview.bs

@@ -325,7 +325,7 @@ The linear gradient syntax is:
 
 	<pre class=prod>
 		<dfn>linear-gradient()</dfn> = linear-gradient(
-			[ <<angle>> | to <<side-or-corner>> ]? ,
+			[ <<zero>> | <<angle>> | to <<side-or-corner>> ]? ,
 			<<color-stop-list>>
 		)
 		<dfn>&lt;side-or-corner></dfn> = [left | right] || [top | bottom]
@@ -338,12 +338,15 @@ The linear gradient syntax is:
 
 	The <a>gradient line's</a> direction may be specified in two ways:
 
-	: using angles
+	: using <<angle>>
+	: using <<zero>>
 	:: For the purpose of this argument,
 		''0deg'' points upward,
 		and positive angles represent clockwise rotation,
 		so ''90deg'' point toward the right.
 
+		<<zero>> points upward (same as ''0deg'').
+
 	: using keywords
 	:: If the argument is ''to top'', ''to right'', ''to bottom'', or ''to left'',
 		the angle of the <a>gradient line</a> is ''0deg'', ''90deg'', ''180deg'', or ''270deg'', respectively.
@@ -1744,9 +1747,12 @@ Interpolating <<gradient>> {#interpolating-gradients}
 	1. Convert both the start and end gradients to their explicit forms:
 
 		: For linear gradients:
-		:: * If the direction is specified as an	<<angle>>,
+		:: * If the direction is specified as an <<angle>>,
 				it is already in its explicit form.
 
+			* If the direction is specified as a <<zero>>,
+				change its direction to ''0deg''.
+
 			* Otherwise,
 				change its direction to an <<angle>> in [''0deg'',''360deg'')
 				that would produce an equivalent rendering.
@@ -1858,7 +1864,7 @@ Thanks to the Webkit team, Brad Kemper, Brian Manthos, and Alan Gresley
 
 	Major changes include:
 
-     
+
     - The ''element()'' feature has been
        deferred to Level 4.
     - The directional images feature (''ltr''/''rtl''
@@ -1874,7 +1880,7 @@ Thanks to the Webkit team, Brad Kemper, Brian Manthos, and Alan Gresley
 
      Significant details updated:
 
-     
+
 	- There is now a definition for <a href="#invalid-image"><i>invalid
        images</i></a>, which trigger fallback in the ''image()'' notation.
     - Clarified that media fragments are only required to be supported
@@ -1889,7 +1895,7 @@ Thanks to the Webkit team, Brad Kemper, Brian Manthos, and Alan Gresley
        be aliased to 'image-fit' and 'image-position'. A future
        edition of the <a href="http://www.w3.org/TR/css-print/">CSS Print
        Profile</a> may allow this for printer implementations, however.
-     
+
 
      There were also many clarifications and several sections were rearranged
       to make them easier to read.

css-transforms-2/Overview.bs

@@ -778,6 +778,9 @@ The value of the 'transform' property is a list of <dfn>&lt;transform-function><
 3D Transform Functions {#three-d-transform-functions}
 ----------------------
 
+In the following functions, a <<zero>> behaves the same as ''0deg''.
+("Unitless 0" angles are preserved for legacy compat reasons.)
+
 
 : <span class='prod'><dfn>matrix3d()</dfn> = matrix3d( <<number>> [, <<number>> ]{15,15} )</span>
 :: specifies a 3D transformation as a 4x4 homogeneous matrix of 16 values in column-major order.
@@ -789,16 +792,16 @@ The value of the 'transform' property is a list of <dfn>&lt;transform-function><
 :: specifies a <a href="#Scale3dDefined">3D scale</a> operation by the [sx,sy,sz] scaling vector described by the 3 parameters.
 : <span class='prod'><dfn>scaleZ()</dfn> = scaleZ( <<number>> )</span>
 :: specifies a <a href="#Scale3dDefined">3D scale</a> operation using the [1,1,sz] scaling vector, where sz is given as the parameter.
-: <span class='prod'><dfn>rotate3d()</dfn> = rotate3d( <<number>> , <<number>> , <<number>> , <<angle>> )</span>
+: <span class='prod'><dfn>rotate3d()</dfn> = rotate3d( <<number>> , <<number>> , <<number>> , [ <<angle>> | <<zero>> ] )</span>
 :: specifies a <a href="#Rotate3dDefined">3D rotation</a> by the angle specified in last parameter about the [x,y,z] direction vector described by the first three parameters. A direction vector that cannot be normalized, such as [0,0,0], will cause the rotation to not be applied.
 
 	Note: the rotation is clockwise as one looks from the end of the vector toward the origin.
 
-: <span class='prod'><dfn>rotateX()</dfn> = rotateX( <<angle>> )</span>
+: <span class='prod'><dfn>rotateX()</dfn> = rotateX( [ <<angle>> | <<zero>> ] )</span>
 :: same as ''rotate3d(1, 0, 0, &lt;angle>)''.
-: <span class='prod'><dfn>rotateY()</dfn> = rotateY( <<angle>> )</span>
+: <span class='prod'><dfn>rotateY()</dfn> = rotateY( [ <<angle>> | <<zero>> ] )</span>
 :: same as ''rotate3d(0, 1, 0, &lt;angle>)''.
-: <span class='prod'><dfn>rotateZ()</dfn> = rotateZ( <<angle>> )</span>
+: <span class='prod'><dfn>rotateZ()</dfn> = rotateZ( [ <<angle>> | <<zero>> ] )</span>
 :: same as ''rotate3d(0, 0, 1, &lt;angle>)'', which is also the same as ''rotate(&lt;angle>)''.
 : <span class='prod'><dfn>perspective()</dfn> = perspective( <<length>> )</span>
 :: 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.

css-transforms/Overview.bs

@@ -591,7 +591,13 @@ The <{linearGradient}> element specifies the <{linearGradient/gradientTransform}
 The Transform Functions {#transform-functions}
 ==============================================
 
-The value of the 'transform' property is a list of <dfn>&lt;transform-function></dfn>. The set of allowed transform functions is given below. Wherever <<angle>> is used in this specification, a <<number>> that is equal to zero is also allowed, which is treated the same as an angle of zero degrees. A percentage for horizontal translations is relative to the width of the 'reference box. A percentage for vertical translations is relative to the height of the [=reference box=].
+The value of the 'transform' property is a list of <dfn>&lt;transform-function></dfn>.
+The set of allowed transform functions is given below.
+In the following functions,
+a <<zero>> behaves the same as ''0deg''
+("unitless 0" angles are preserved for legacy compat).
+A percentage for horizontal translations is relative to the width of the [=reference box=].
+A percentage for vertical translations is relative to the height of the [=reference box=].
 
 2D Transform Functions {#two-d-transform-functions}
 ----------------------
@@ -618,17 +624,17 @@ The value of the 'transform' property is a list of <dfn>&lt;transform-function><
 	: <span class='prod'><dfn>scaleY()</dfn> = scaleY( <<number>> )</span>
 	:: specifies a <a href="#ScaleDefined">2D scale</a> operation using the [1,sy] scaling vector, where sy is given as the parameter.
 
-	: <span class='prod'><dfn>rotate()</dfn> = rotate( <<angle>> )</span>
+	: <span class='prod'><dfn>rotate()</dfn> = rotate( [ <<angle>> | <<zero>> ] )</span>
 	:: specifies a <a href="#RotateDefined">2D rotation</a> by the angle specified in the parameter about the origin of the element, as defined by the 'transform-origin' property. For example, ''rotate(90deg)'' would cause elements to appear rotated one-quarter of a turn in the clockwise direction.
 
-	: <span class='prod'><dfn>skew()</dfn> = skew( <<angle>> [, <<angle>> ]? )</span>
+	: <span class='prod'><dfn>skew()</dfn> = skew( [ <<angle>> | <<zero>> ] [, [ <<angle>> | <<zero>> ] ]? )</span>
 	:: specifies a <a href="#SkewDefined">2D skew</a> by [ax,ay] for X and Y. If the second parameter is not provided, it has a zero value.
     	<p class="note">Note that the behavior of ''skew()'' is different from multiplying ''skewX()'' with ''skewY()''. Implementations must support this function for compatibility with legacy content.
 
-	: <span class='prod'><dfn>skewX()</dfn> = skewX( <<angle>> )</span>
+	: <span class='prod'><dfn>skewX()</dfn> = skewX( [ <<angle>> | <<zero>> ] )</span>
 	:: specifies a <a href="#SkewXDefined">2D skew transformation along the X axis</a> by the given angle.
 
-	: <span class='prod'><dfn>skewY()</dfn> = skewY( <<angle>> )</span>
+	: <span class='prod'><dfn>skewY()</dfn> = skewY( [ <<angle>> | <<zero>> ] )</span>
 	:: specifies a <a href="#SkewYDefined">2D skew transformation along the Y axis</a> by the given angle.
 
 </dl>

css-values/Overview.bs

@@ -709,6 +709,13 @@ Real Numbers: the <<number>> type</h3>
 	As with integers, the first character of a number may be immediately preceded by ''-'' or ''+''
 	to indicate the number's sign.
 
+	The value <dfn id=zero-value>&lt;zero></dfn> represents a literal <a>number</a>
+	with the value 0.
+	Expressions that merely evaluate to a <<number>> with the value 0
+	(for example, ''calc(0)'')
+	do not match <<zero>>;
+	only literal <<number-token>>s do.
+
 <!--
 █████   ██
 ██ ██  ██
@@ -1273,8 +1280,6 @@ Other Quantities</h2>
 Angle Units: the <<angle>> type and ''deg'', ''grad'', ''rad'', ''turn'' units</h3>
 
 	Angle values are <<dimension>>s denoted by <dfn id="angle-value">&lt;angle></dfn>.
-	However, for zero angles the unit identifier is optional
-	(i.e. can be syntactically represented as the <a>number</a> ''0'').
 	The angle unit identifiers are:
 
 	<dl export dfn-type=value dfn-for="<angle>">
@@ -1315,6 +1320,11 @@ Angle Units: the <<angle>> type and ''deg'', ''grad'', ''rad'', ''turn'' units</
 		is interpreted as a bearing angle.
 	</div>
 
+	Note: For legacy reasons,
+	some uses of <<angle>> allow a bare ''0'' to mean ''0deg''.
+	This is not true in general, however,
+	and will not occur in future uses of the <<angle>> type.
+
 <!--
 ████████ ████ ██     ██ ████████
    ██     ██  ███   ███ ██
@@ -1670,7 +1680,7 @@ Type Checking</h4>
 	An ''attr()'' expression's type is given by its <<type-or-unit>> argument.
 
 	Note: Because <<number-token>>s are always interpreted as <<number>>s or <<integer>>s,
-	"unitless 0" <<length>>s or <<angle>>s aren't supported in ''calc()''.
+	"unitless 0" <<length>>s aren't supported in ''calc()''.
 	That is, ''width: calc(0 + 5px);'' is invalid,
 	even though both ''width: 0;''
 	and ''width: 5px;''