Complex sentence: The "tankōbon" format has made inroads in the American comics market, with several major publishers opting to release some of their titles in this smaller format, which is sometimes also called "digest format" or "digest size".
Split into simpler sentences: The "tankōbon" format has made inroads in the American comics market, with several major publishers opting to release some of their titles in this smaller format. This format is also called "digest format" or "digest size".