Volume of the journal in which a related article exists
It is best practice to limit the scope of this attribute to the current journal, i.e., the one in which the current article also resides.
|Text, numbers, or special characters
|The journal volume number for a related article, for example, “3” for the third volume, “125” for the one hundred and twenty-fifth, or “XV” for the fifteenth
|Restriction: This attribute may be specified if the element is used.