[css-shapes-2] Add detailed example for

css-shapes-2/Overview.bs

@@ -318,7 +318,7 @@ The ''shape()'' Function</h4>
 			the command's starting point, the command's end point, or the [=reference box=], respectively.
 			If such component is not provided, the <<coordinate-pair>> is relative to the segment's start.
 
-		<dt><dfn><<arc-command>></dfn> = <dfn value>arc</dfn> <<command-end-point>> [[of <<length-percentage>>{1,2}] && <<arc-sweep>>? && <<arc-size>>? && rotate <<angle>>? ]
+		<dt><dfn><<arc-command>></dfn> = <dfn value>arc</dfn> <<command-end-point>> [[of <<length-percentage>>{1,2}] && <<arc-sweep>>? && <<arc-size>>?|| rotate <<angle>>? ]
 		<dd>
 			Add an <a href="https://www.w3.org/TR/SVG/paths.html#PathDataEllipticalArcCommands">elliptical arc</a> command
 			to the list of path data commands,
@@ -406,6 +406,127 @@ The ''shape()'' Function</h4>
 			which affects how line-joins and line-caps are rendered.
 	</dl>
 
+<h5 id=shape-examples>Using ''shape()'' to create responsive, parametric speech bubble</h5>
+
+<div class=example>
+The ''shape()'' function enables shapes that are responsive, rather than scalable.
+While the ''polygon()'' shape is also responsive, it doesn't support curves.
+
+To demonstrate, let's start with a speech bubble, such as the following:
+
+<img src="images/bubble.svg" width=300 style="background: unset">
+
+Using this shape with a ''clip-path'' can be done by using the ''path()'' function:
+
+<pre highlight="css">
+.bubble { clip-path: path("m 5 0 H 95 Q 100 0 100 5 V 92 Q 100 97 95 97 H 70 l -2 3 l -2 -3 H 5 Q 0 97 0 92 V 5 Q 0 0 5 0") };
+</pre>
+
+Altohugh this path can easily scale, the scaled results are not always desirable. e.g. when scaled to a small balloon, the arrow and corners are scaled to become almost invisible:
+
+<img src="images/bubble.svg" width=100 style="background: unset">
+
+To construct this shape using the ''shape()'' function, let's start by turning all the pixel values from the ''path'' function to percentages.
+Note that the ''shape()'' function begins with <css>from</css>:
+
+<pre highlight="css">
+.bubble { clip-path: shape(	from 5% 0%,
+							hline to 95%,
+							curve to 100% 5% with 100% 0%,
+							vline to 92%,
+							curve to 95% 97% with 100% 97%,
+							hline to 70%,
+							line by -2% 3%,
+							line by -2% -3%,
+							hline to 5%,
+							curve to 0% 92% with 0% 97%,
+							vline to 5%,
+							curve to 5% 0% with 0% 0%); }
+</pre>
+
+To make this path responsive, as in, respond well to size changes, we will convert some of its units to ''px'' values,
+specifically the ones the control the curves and arrows:
+
+<pre highlight="css">
+.bubble { clip-path: shape(	from 5px 0%,
+							hline to calc(100% - 5px),
+							curve to 100% 5px with 100% 0%,
+							vline to calc(100% - 8px),
+							curve to calc(100% - 5px) calc(100% - 3px) with 100% calc(100% - 3px),
+							hline to 70%,
+							line by -2px 3px,
+							line by -2px -3px,
+							hline to 5px,
+							curve to 0% calc(100% - 8px) with 0% calc(100% - 3px),
+							vline to 5px,
+							curve to 5px 0% with 0% 0%); }
+</pre>
+
+When applied as ''clip-path'', it would looks like the following:
+<p>
+<img src="images/bubble-50.svg" width=150 style="background: unset">
+</p>
+
+The whole speech bubble is scaled to the reference box, while the curves and arrows stay more constant.
+
+Since ''shape()'' uses CSS units, we can replace some of the edges with ''position'' values:
+
+<pre highlight="css">
+.bubble { clip-path: shape(from 5px 0,
+							hline to calc(100% - 5px),
+							curve to right 5px with right top,
+							vline to calc(100% - 8px),
+							curve to calc(100% - 5px) calc(100% - 3px) with right calc(100% - 3px),
+							hline to 70%,
+							line by -2px 3px,
+							line by -2px -3px,
+							hline to 5px,
+							curve to left calc(100% - 8px) with left calc(100% - 3px),
+							vline to 5px,
+							curve to 5px top with left top); }
+</pre>
+
+Another useful feature of ''shape()'' is that it can be used alongside CSS properties. In this case,
+we can make the arrow and radius parametric, and even animate them:
+
+<pre highlight="css">
+
+@keyframes bubble {
+	from {
+		--radius: 30px;
+		--arrow-position: 20%;
+	}
+}
+
+:root {
+	--radius: 5px;
+	--arrow-length: 3px;
+	--arrow-half-width: 2px;
+	--arrow-position: 70%;
+	--arrow-bottom-offset: calc(100% - var(--radius) - var(--arrow-length));
+}
+
+.bubble {
+	animation: bubble 100ms;
+	clip-path: shape(from var(---radius) top,
+		hline to calc(100% - var(---radius)),
+		curve to right var(---radius) with right top,
+		vline to var(---arrow-bottom-offset),
+		curve to calc(100% - var(---radius)) calc(100% - var(---arrow-length))
+              with right calc(100% - var(---arrow-length)),
+		hline to var(---arrow-position),
+		line by var(---arrow-half-width) var(---arrow-length),
+		line by var(---arrow-half-width) calc(0px - var(---arrow-length)),
+		hline to var(---radius),
+		curve to left var(---arrow-bottom-offset) with left calc(100% - var(---arrow-length)),
+		vline to var(---radius),
+		curve to var(---radius) top with left top); }
+</pre>
+
+
+
+</div>
+
 <h5 id=interpolating-shape>
 Interpolating the ''shape()'' Function</h5>