@asciidoctor/core
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    Variable SERVER

    SERVER: number

    A safe mode level that disallows the document from setting attributes that would affect the conversion of the document, in addition to all the security features of SafeMode.SAFE. For instance, this level forbids changing the backend or source-highlighter using an attribute defined in the source document header. This is the most fundamental level of security for server deployments (hence the name).