It appears that the Java SE team have moved their "Extension Architecture" documentation. This invalidates the link in the CDI JavaDocs we publish as follows:
In the file:
cdi-api-1.2-sources\javax\enterprise\inject\Vetoed.java
Is a link in the meta data for JavaDoc:
<a href="http://download.java.net/jdk8/docs/technotes/guides/extensions/spec.html#sealing">
Which returns <404>, file not found.

I suspect this is now moved to:
https://docs.oracle.com/javase/8/docs/technotes/guides/extensions/spec.html

But I can't be sure because there's no Anchor titled "sealing" in that moved document.