org-property-allowed-value-functions

org-property-allowed-value-functions is a variable defined in `org.el'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
Hook for functions supplying allowed values for a specific property.
The functions must take a single argument, the name of the property, and
return a flat list of allowed values. If ":ETC" is one of
the values, this means that these values are intended as defaults for
completion, but that other values should be allowed too.
The functions must return nil if they are not responsible for this
property.