This new feature identifies port-based rules so you can convert them to application-based rules that allow the traffic or add applications to existing rules without compromising application availability.
https://docs.paloaltonetworks.com/pan-os/10-2/pan-os-admin/app-id/security-policy-rule- optimization

Virtual wire interfaces by default allow all untagged traffic. You can, however, use a virtual wire to connect two interfaces and configure either interface to block or allow traffic based on the virtual LAN (VLAN) tags. VLAN tag 0 indicates untagged traffic.
You can also create multiple subinterfaces, add them into different zones, and then classify traffic according to a VLAN tag or a combination of a VLAN tag with IP classifiers (address, range, or subnet) to apply granular policy control for specific VLAN tags or for VLAN tags from a specific source IP address, range, or subnet.
https://docs.paloaltonetworks.com/pan-os/10-1/pan-os-networking-admin/configure- interfaces/virtual-wire-interfaces/virtual-wire-subinterfaces

"A "heartbeat-interval" CLI command was added to the election settings for HA, this interval has a
1000ms minimum for all Palo Alto Networks platforms and is an ICMP ping to the other device through the HA control link."
https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClUcCAK