Add a Historical section discussing old interfaces

Fixes #163.

Author: zcorpan

geometry/Overview.bs

@@ -2063,6 +2063,38 @@ specification could potentially introduce security or privacy issues.
 </div>
 
 
+<h2 id="historical">Historical</h2>
+
+<p>The interfaces in this specification are intended to replace earlier similar interfaces found in
+various specifications as well as proprietary interfaces found in some user agents. This section
+attempts to enumerate these interfaces.
+
+
+<h3 id="historical-cssom">CSSOM</h3>
+
+<p>Earlier revisions of CSSOM defined a <code>ClientRect</code> interface, which is replaced by
+{{DOMRect}}. Implementations conforming to this specification will not support
+<code>ClientRect</code>. [[CSSOM]]
+
+
+<h3 id="historical-svg">SVG</h3>
+
+<p>Earlier revisions of SVG defined {{SVGPoint}}, {{SVGRect}}, {{SVGMatrix}}, which are defined in
+this specifications as aliases to {{DOMPoint}}, {{DOMRect}}, {{DOMMatrix}}, respectively. [[SVG11]]
+
+
+<h3 id="historical-non-standard">Non-standard</h3>
+
+<p>Some user agents supported a <code>WebKitPoint</code> interface. Implementations conforming to
+this specification will not support <code>WebKitPoint</code>.
+
+<p>Several user agents supported a {{WebKitCSSMatrix}} interface, which is also widely used on the
+Web. It is defined in this specification as an alias to {{DOMMatrix}}.
+
+<p>Some user agents supported a <code>MSCSSMatrix</code> interface. Implementations conforming to
+this specification will not support <code>MSCSSMatrix</code>.
+
+
 <h2 class="no-num" id="changes">Changes since last publication</h2>
 
 <p>The following changes were made since the <a