We want User objects. The second expression is used to qualify the User object's Surname attribute. In our example, the search user may not know exactly what the last name of his target user, so we want NDS to make an approximation of equality. See Table 1 for a list of possible filter tokens. As you can see, some tokens contain values.
Equals is a relational operator token.
Relational operator tokens contain no values but express a relationship between two tokens that do. Another example of a relational token would be less than or equal to. Two subexpressions can be joined together with a logical operator token like AND expressing a logical relationship between subexpressions or values. There are also tokens signifying parentheses, which can be used to group subexpressions or values. Stores values which are binary strings.