xref:Lucene.Net.Expressions.Expression - result of compiling an expression, which can evaluate it for a given document. Each expression can have external variables are resolved by {@code Bindings}.
xref:Lucene.Net.Expressions.Bindings - abstraction for binding external variables to a way to get a value for those variables for a particular document (ValueSource).
xref:Lucene.Net.Expressions.SimpleBindings - default implementation of bindings which provide easy ways to bind sort fields and other expressions to external variables