大般涅槃經義記 1.184

1.184

就明空中，「有道性相一切空」者，三有、六道因緣虛集，求其性相一切空也。假中無性，名為性空。緣假亦無，名為相空。

Regarding the explanation of emptiness, "the nature and marks of the paths of existence are entirely empty" means that the three existences and six paths are falsely gathered by causes and conditions; when seeking their nature and marks, they are entirely empty. Being without nature within the nominal is called nature-emptiness. Conditioned nominalities also being non-existent is called mark-emptiness.