${XPATH}
$[{XPath}]
${parent::*}.AddGround(...)
${parent::*}.AddSigner(...)
${parent::*}.AddLink(...)

_Signatures
_Grounds
_Links
_SignedBy
_Sources
_isPrimary

argument | function_call
function_call(argument)
object.Property
list[item]
list[.Property=value]

_loader
_validator
self

new
assert
claim

foreach ... in ...
if ... elif ... else ...

-union -intersect

-eq -ne -ge -le -ls -gr
-not -and -or
-iselement -issubset

-istype

System