<leafNode name="table-size">
  <properties>
    <help>Maximum number of entries to keep in the ARP cache</help>
    <completionHelp>
      <list>1024 2048 4096 8192 16384 32768</list>
    </completionHelp>
    <constraint>
      <regex>(1024|2048|4096|8192|16384|32768)</regex>
    </constraint>
  </properties>
</leafNode>

$ cat /opt/vyatta/share/vyatta-cfg/templates/system/ip/arp/table-size/node.def
type: txt
help: Maximum number of entries to keep in the ARP cache
allowed: echo "1024 2048 4096 8192 16384 32768"
syntax:expression: exec "${vyos_libexec_dir}/validate-value.py --regex \'(1024|2048|4096|8192|16384|32768)\'  --value \'$VAR(@)\'"; "Invalid value"

vyos@vyos# set system ip arp table-size
Possible completions:
   <text>       Maximum number of entries to keep in the ARP cache
   1024
   16384
   2048
   32768
   4096
   8192