This schema provides for creating relationships between items identified by Crossref DOIs, non-Crossref DOIs, and other identifiers. See: https://support.crossref.org/hc/en-us/articles/214357426
Wrapper element for relationship metadata
Description of the relationship to the target item or of the target item itself
Used to describe relations between items that are not the same work.
Used to define relations between items that are essentially the same work but may differ in some way that impacts citation, for example a difference in format, language, or revision. Assigning different identifers to exactly the same item available in one place or as copies in multiple places can be problematic and should be avoided.
An identifier systems may require a namespace that is needed in addition to the identifer value to provide uniqueness.
A narrative description of the relationship target item
Basic data types for face markup in the target related item
Language attributes are based on ISO 639