Volume Number
When an Release is part of a series, the VolumeNumber is the part of the ReleaseTitle that describes the position in the series. It usually takes the form Volume x, but other words are used too.
VolumeNumbers follow VolumeNumberStyle.
Note that a VolumeNumber is not the same as a DiscNumber. VolumeNumbers are usually added to releases that are not released together and not on the same date; DiscNumbers indicate releases are part of a multi disc release, sold as one item.
Examples
ReleaseTitle: "Greatest Hits of 1993, Volume 3"
VolumeNumber: "Volume 3"
ReleaseTitle: "Cool Songs, Chapter Four"
VolumeNumber: "Chapter Four"
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