Defined in file entrez2.asn
C++ class: CEntrez2_boolean_element
Entrez2-boolean-element ::= CHOICE {
str VisibleString , -- unparsed query string
op Entrez2-operator , -- logical operator
term Entrez2-boolean-term , -- fielded term
ids Entrez2-id-list , -- list of UIDs - returns history key in reply
key VisibleString } -- history key for uploaded UID list or other query