Function validate_dns1123_name 

pub fn validate_dns1123_name(value: &str, field: &str) -> ValidationResult

A DNS-1123 subdomain (the shape of every Kubernetes object name): non-empty, ≤253 chars, lowercase alphanumerics / - / ., starting and ending alphanumeric. The structural schema can’t express it, so the webhook does. field names where the value appears, for an actionable message.