The documentation comes from the Markdown files in the source code, so is always up-to-date but available only in English. Enjoy!
Expression Visitor is able to detect constant subtrees of an expression tree that could potentially be replaced by just a value. This capability is what allows that IQueryable Linq queries blur the boundaries between your code and, presumably, SQL.
public class ExpressionNominator : ExpressionVisitor
public static HashSet<Expression> Nominate(Expression expression)