What are environment variables "BASH_FUNC_somename%%"?

Issue

• I see environment variables similar to "BASH_FUNC_somename%%", what are they and what are they for?

  > env | grep '%%'
  BASH_FUNC_which%%=() {  ( alias;
  BASH_FUNC_module%%=() {  _module_raw "$@" 2>&1
  ...