Creating a trigger prototype based on two item prototypes?

[tmroberts]

I'm trying to create a set of trigger prototypes in a Cisco template to evaluate two port channel pairs based on the Operational Status or the port channels. If one or the other is down it would trigger a high alert. If both are down it would trigger a critical alert. The problem is I'm drawing a complete blank on how to do this. Here is what the template is currently creating when it discovers the interfaces:

Template Macros:
{$SEV_INFO} = ^Server
{$SEV_MOD} = ^Link to
{$SEV_WARN} = (PDU-|WAP-|ATS-|UPS-)

Item Prototypes that I'd like to use:
Name: Operational status of interface $1
Key: ifOperStatus[{#SNMPVALUE}] (value of 1 means its up, 2 means its down)

Trigger Prototypes (that currently exist):
Low Trigger: {Template App SNMPv3 Cisco Interfaces - Access Devices:ifAlias[{#SNMPVALUE}].regexp({$SEV_WARN})}=1 and {Template App SNMPv3 Cisco Interfaces - Access Devices:ifOperStatus[{#SNMPVALUE}].diff(0)}>0
Med Trigger: {Template App SNMPv3 Cisco Interfaces - Access Devices:ifAlias[{#SNMPVALUE}].regexp({$SEV_MOD})}=1 and {Template App SNMPv3 Cisco Interfaces - Access Devices:ifOperStatus[{#SNMPVALUE}].diff(0)}>0

So here are my questions:

1. In both of the trigger expressions above they are using a regexp against the macros associated with the template. I guess i'm not fully understanding how those are working. Is it if the regex = the value its a 1? Can someone please explain what is happening there?
2. To me it looks like these triggers are evaluating the severity of the "error" for the interface rather than if its just up/down. If that's the case can I just get rid of the first half of the expression and just evaluate if the port is up or down?
3. These triggers are using the SNMPVALUE as the macro, but I am only interested in a couple of ports that get discovered (i.e. TenGigabitEthernet5/1 and TenGigabitEthernet6/1). I want to create triggers for the following scenarios:
   1. TenGigabitEthernet5/1 is up but TenGigabitEthernet6/1 is down (or vise versa)
   2. TenGigabitEthernet5/1 AND TenGigabitEthernet6/1 are down.

Any help is much appreciated.