New example for intro to "Web Media APIs currently supported on all p…

…latforms" (#326)

Replaced Push API with CSS Images Module Level 4

index.html

@@ -180,7 +180,7 @@ <h2>Web Media APIs currently supported on all platforms</h2>
         <h2>Introduction</h2>
         <p>This section lists the web APIs to support media web apps that are supported across all four of the most widely used user agent code bases at the time of publication (i.e., Chrome, Edge, Firefox, and Safari). We encourage manufacturers to develop products that support the APIs in the most recent version of this specification.</p>
         <p>The approach taken in this draft is only to include specifications that are of particular significance to authors, but not include all the specifications cited by those included specifications. For example, HTTP is required by the HTML spec and is therefore not included here.</p>
-        <p>In addition, the specifications of the web APIs mentioned here may in turn (recursively) reference other specifications that are not supported across all four of the most widely used user agent code bases. This possibility is understood and accepted. For example, Service Workers 1 [[SERVICE-WORKERS-1]] references the <code>push</code> event from the Push API [[PUSH-API]], but the Push API is not yet widely supported. These unsupported referenced specifications are not explicitly cited as exceptions in this specification but, in spite of this, will not be tested as part of our tests.</p>
+        <p>In addition, the specifications of the web APIs mentioned here may in turn (recursively) reference other specifications that are not supported across all four of the most widely used user agent code bases. This possibility is understood and accepted. For example, Content Security Policy Level 2 [[CSP2]] references the <code>image()</code> function from CSS Images Module Level 4 [[CSS-IMAGES-4]], but CSS Images Module Level 4 is not yet widely supported. These unsupported referenced specifications are not explicitly cited as exceptions in this specification but, in spite of this, will not be tested as part of our tests.</p>
         <section>
           <h3>Features with limited implementation</h3>
           <p>Parts of some web specifications are not currently implemented across all user agent code bases and may never be. Consequently, these features will not be included in our tests. Any such features are noted as exceptions under that API.</p>