How to access iPXE option-space sub-options ?

Hello! I've recently discovered ISC Kea and I am LOVING it, really <3

In ISC DHCPd, I would declare the option space like this:

# Declare the iPXE option space
option space ipxe;
option ipxe-encap-opts code 175 = encapsulate ipxe;

# iPXE options, can be set in DHCP response packet
option ipxe.priority code 1 = signed integer 8;

# iPXE feature flags, set in DHCP request packet
option ipxe.nfs code 41 = unsigned integer 8;

I tried declaring it in ISC Kea like that, from what I could find in the docs that resembled it a bit:

{
   "Dhcp4": {
      "option-def": [
            {
                "name": "nfs",
                "code": 41,
                "space": "ipxe",
                "type": "uint8"
            },

            {
                 "name": "container",
                 "code": 175,
                 "space": "dhcp4",
                 "type": "empty",
                 "array": false,
                 "encapsulate": "ipxe"
            }
      ]
   }
}

In reality, I only want to check if ipxe.nfs is equal to 1 to see if my client has NFS-boot possibilities.

In ISC DHCPd, I would check like that:

if exists user-class and option user-class = "iPXE" and exists ipxe.nfs {
   # do stuff
}

I tried the following in ISC Kea (client-class) but I have to admit that I am kind of lost:

{
   "name": "iPXE",
   "test": "(substring(option[77].hex,0,4) == 'iPXE') and (option[41].exists)",
   "boot-file-name": "http://192.168.136.112/boot.ipxe"
},

I tried a bunch of stuff, but no success..

Note that (substring(option[77].hex,0,4) == 'iPXE') on it's own functions properly.

PS: Can we have multiple test fields instead of chaining ands?