copy-to-clipboard clipboard icon doesn't appear using file: urls
At least on chrome, viewing a site with source blocks. the dev tools console shows an error:
06-copy-to-clipboard.js:38 Unsafe attempt to load URL file:///Users/david/projects/antora/simple-examples/extensions/tabset-block-extension/build/site/_/img/octicons.svg#symbol-clippy-16 from frame with URL file:///Users/david/projects/antora/simple-examples/extensions/tabset-block-extension/build/site/c1/1.0/other.html. 'file:' URLs are treated as unique security origins.
and the clipboard icon doesn't appear. However, clicking where it should be does copy the source :-).
It looks like it's possible to sidestep this security policy by showing the icon via css, e.g.
.doc .source-toolbox .copy-button {
...
/*background: transparent;*/
background: url(../img/octicons.svg#symbol-clippy-16) no-repeat 50% 50%;
...
(this isn't the right size yet)