Configure a tagged and untagged interface on a Juniper SRX (100)

set interfaces fe-0/0/0 flexible-vlan-tagging
set interfaces fe-0/0/0 unit 0 vlan-id 20
set interfaces fe-0/0/0 unit 0 family ethernet-switching port-mode trunk
set interfaces fe-0/0/0 unit 0 family ethernet-switching vlan members tagged_vlan
set interfaces fe-0/0/0 unit 0 family ethernet-switching native-vlan-id 20