$is is the universal inverse restriction

$   <-- Pattern: Context Self Descriptor -->
        $is$a
                ($xdi$v$1)      <-- Pattern: Context Type -->
                ($pdx$v$1)

        $is($xdi$v$1)   <-- Pattern: Context Authority -->
                =!1111.aaaa.bbbb.cccc!9999.xxxx.yyyy.zzzz