pcs reports "Error: unknown cluster property" when attempting to set the "site-name" cluster property

Issue

• pcs reports "Error: unknown cluster property" when attempting to set the site-name cluster property
• Why do I have to use the --force option to set the site-name property?
• The site-name cluster property is not taking updating the #site-name node attribute.

# pcs property set site-name=TEST
Error: unknown cluster property: 'site-name', (use --force to override)