version 1 .

Expr =
/ @steps [Step ...]
/ <not @expr Expr>
/ <interleave @exprs [Expr ...]>
/ <union @exprs [Expr ...]>
/ <intersection @exprs [Expr ...]>
.

Step = Axis / Filter / Expr .

Axis =
/ <nop>
/ <values>
/ <descendants>
/ <at @key any>
/ <label>
/ <keys>
/ <length>
/ <annotations>
/ <embedded>
.

Filter =
/ <nop>
/ <fail>
/ <eq @literal any>
/ <regex @regex string>
/ <test @expr Expr>
/ <kind @kind ValueKind>
.

ValueKind =
/ =Boolean / =Float / =Double / =SignedInteger / =String / =ByteString / =Symbol
/ =Record / =Sequence / =Set / =Dictionary
/ =Embedded
.