Along with Rules, an meta-model must define one or several filters. Projections are actually the result of filters applied to the rules of the project; they permit to show only chosen aspects of the project by creating specific views on it. For instance, in a systems engineering project your projections could include System Architecture, Functional Architecture and Physical Architecture as well as Use Cases. You can learn more about the functioning of filtering from Filtering Principles.
After having defined Rules, you need to create at least one filter (and therefore at least one projection) for your project. Each project can have several filters, each allowing you to focus on specific parts of it. The filters are actually applied to rules and not to types (for more information on the difference between rules, types and type relations see the Types and Type Relations). It is therefore possible to choose to display a type in a given context while excluding other contexts: for instance, it is possible to display all Cars that are children of the Transport System but to exclude the ones that are children of Consumer Goods.
You need to define (or at least to start to define) Rules before you can start defining filters.
To access the Filters part of the meta-model, click on the Filters section in Rules and Filters. If the Rules and Filters panel is not visible, you can display it with Rules and Filters in the Show / Hide Panel of the Tools Category. If you are currently viewing Rules, look for Filters at the bottom of the panel.
Filters lists all the existing filters in alphabetical order, filter folders first and filters next. The filter order cannot be modified.