Just a little disclaimer.
Keep in mind that only size, rotate and flip are officially supported. Other features like border or spin, even when they can be "achieved", it's done with a side effect of the implementation. That's why I filed the issue on GitHub, to discuss what should be the correct behauviour.
Also, don't forget this applies to HTML conversion.
patrickm wrote
This works:
icon:heart[border]
According to documentation (
http://asciidoctor.org/docs/user-manual/#size-rotate-and-flip), the first attribute is by default the size. Again, due to how it is implemented, you can apply some styles, but this is not made on purpouse, or at least seeing the code it does not seem to me like that.
Until Dan says something about this, I would try to avoid them and stick to the official supported features.