This article talks about the ActiveDEMAND query engine. The AD query engine is used in workflow decisions, dynamic content queries, contact list segregation, etc.
The query builder is very powerful. The UI is designed to simplify the process of creating complex logic. The builder allows for 3 sets of nested braces. ((())) … almost. All logic within a group must have the same boolean operator. Thus you get a choice, AND or OR for a group, no combination of such. Thus group(Filter 1 and Filter 2 and Filter 3). This same rule applies within a block. Group 1and Group 2 and Group 3. As you can imagine this is also true for blocks. Block 1 or Block 2 or Block 3. Thus it is not possible to do Filter 1 and Filter 2 or Filter 3 as combining and/or within a logic grouping is not possible.
The query builder is probably the most powerful and hence most complex aspect of ActiveDEMAND.
This article here is a better overview :