Cross-reference (xref) label
When the xref is bidirectional, the same label is associated with both directions.
To avoid confusion, the convention is to name the label in relation to the forward direction. For example, if a label is used to express a parent/child relationship between A and B, A being the parent and A linking to B, then name the label as ‘child’. If B linked to A, then name the label as ‘parent’.
The source document refers to the document containing the original xref in its content. The target document refers to document being pointed at.