Better document what happens when in/outputting CellId objects.
Better document what happens when in/outputting CellId objects.

EGP-CIG-REU/dealii,spco/dealii,shakirbsm/dealii,JaeryunYim/dealii,kalj/dealii,EGP-CIG-REU/dealii,sairajat/dealii,naliboff/dealii,shakirbsm/dealii,shakirbsm/dealii,angelrca/dealii,EGP-CIG-REU/dealii,angelrca/dealii,jperryhouts/dealii,EGP-CIG-REU/dealii,sairajat/dealii,EGP-CIG-REU/dealii,kalj/dealii,EGP-CIG-REU/dealii,kalj/dealii,pesser/dealii,spco/dealii,pesser/dealii,shakirbsm/dealii,jperryhouts/dealii,danshapero/dealii,naliboff/dealii,shakirbsm/dealii,danshapero/dealii,naliboff/dealii,spco/dealii,naliboff/dealii,pesser/dealii,JaeryunYim/dealii,kalj/dealii,JaeryunYim/dealii,jperryhouts/dealii,naliboff/dealii,angelrca/dealii,pesser/dealii,danshapero/dealii,jperryhouts/dealii,spco/dealii,sairajat/dealii,sairajat/dealii,jperryhouts/dealii,JaeryunYim/dealii,sairajat/dealii,spco/dealii,sairajat/dealii,shakirbsm/dealii,EGP-CIG-REU/dealii,JaeryunYim/dealii,kalj/dealii,JaeryunYim/dealii,naliboff/dealii,angelrca/dealii,pesser/dealii,danshapero/dealii,sairajat/dealii,jperryhouts/dealii,spco/dealii,angelrca/dealii,shakirbsm/dealii,danshapero/dealii,angelrca/dealii,pesser/dealii,pesser/dealii,jperryhouts/dealii,kalj/dealii,naliboff/dealii,angelrca/dealii,kalj/dealii,danshapero/dealii,danshapero/dealii,JaeryunYim/dealii,spco/dealii