sibling

Hypertext links in HTML (draft)

      SIBLING
         The SIBLING relationship identifies a sibling in the current
         hierarchy. Any document may have multiple SIBLING documents
         within the same hierarchy.

         When REL=SIBLING, the target document is a child of a common
         parent, or a hierarchical peer of the current document.  REL
         and REV have equivalent meanings for the SIBLING
         relationship.

[引用： 4.4d. Hierarchy Links -- Hypertext links in HTML (draft) より]