dnscontrol/docs/_functions/domain/DnsProvider.md

name	parameters
DnsProvider	name nsCount

DnsProvider indicates that the specifid provider should be used to manage records for this domain. The name must match the name used with NewDnsProvider.

The nsCount parameter determines how the nameservers will be managed from this provider.

Leaving the parameter out means "fetch and use all nameservers from this provider as authoritative". ie: DnsProvider("name")

Using 0 for nsCount means "do not fetch nameservers from this domain, or give them to the registrar".

Using a different number, ie: DnsProvider("name",2), means "fetch all nameservers from this provider, but limit it to this many.

See this page for a detailed explanation of how DNSControl handles nameservers and NS records.