Function is_valid_namespace 

pub fn is_valid_namespace(name: &str) -> bool

Returns true if name is a valid namespace identifier of either kind (registered name or vendor domain name).

Equivalent to is_registered_namespace(name) || is_vendor_namespace(name).

use jmap_metadata_types::is_valid_namespace;

assert!(is_valid_namespace("photography"));
assert!(is_valid_namespace("acme.example.com"));
assert!(!is_valid_namespace(""));
assert!(!is_valid_namespace("has space"));