{attribute}
should be defined.
If it is not defined, AsciiDoc will usually print it as is in the output. Having an undefined attribute in the source might indicate a mis-spelled attribute.
To print a text in curly brackets as is, mark it as pass through content like +{attribute}+
An attribute will be treated as defined if it is declared in at least one of the following places:
.asciidoctorconfig
or .asciidoctorconfig.adoc
file in the current project.{table-caption}
or {docname}
.