<xray-selection> :==
(
<lvflc>
[
<logical-operator>
<xray-selection>
] )
<lvflc> :==
all
|
none
|
true
|
false
|
<relation>
<relation> :==
<xray-expression>
<relational-operator>
<xray-expression>
<relational-operator> :==
= | # | > | >= | < | <=
<logical-operator> :==
and
|
or
|
not