What happens if a human and an elf have a planetouched (i.e.: aasimar or tiefling) child together? How do you stat up the resulting character? Normally, a half-elf would be a human with the half-elf heritage, and an planetouched would be a heritage added to any normal race in a similar fashion. The half-elf and planetouched options provide low-light vision, although the planetouched can also upgrade low-light vision to darkvision. Different racial feats are opened up, with the half-elf granting elf and half-elf options, and the planetouched having its own selection (split into aasimar and tiefling options).
For that matter, what happens if an aasimar and a tielfing have a kid together?
Ugh. A person could go crazy thinking about this.