Game mechanics for the realm are identical to the half-elf race detailed in the D&D 4e official rulebooks, except as noted below. For all other mechanical purposes (including feats, paragon paths, etc.), realm is simply an alternative name for half-elf.
Cosmopolitan: Choose a heritage other than realm. For all race-based effects and requirements, you are considered to have the chosen heritage, as well as realm. This benefit replaces Dual Heritage.