Just note that Asciidoctor provides a set of pre-defined attributes that are used to setup some configurations (eg. `images` for images directory path).
So, make sure you don't use a name that already exists.
Also, you can set pass them as a command argument `asciidoctor -a LY=liyan document.adoc` if you want to set the value outside of the document. The Maven and Gradle plugins allow to set them in the build configuration.