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# CEL in the User Interface

In the UI, a standard CEL Widget interface is provided for CEL expressions. For your convenience, this allows you to build CEL expressions out of three different types of components (called statements):

• Paths – these are explicit lists of scene graph paths. If you drag and drop locations from the Scene Graph tab onto the Add Statements area of the CEL widget you are automatically given a CEL expression that based on those paths.

• Collections – a pre-defined named collection of scene graph locations. Essentially these are arbitrary sets of locations that are handed off for use downstream in the pipeline. Collections can be created in a Katana scene using the CollectionsCreate node, and can also be passed from one Katana project to another using Look Files.

• Custom – these allow complex rule based expressions, such as using patterns with wildcards in the paths, or 'value expressions' that specify values that attributes must have for matches.

CEL expressions can also be built out of combinations of these components using union, difference, and intersection operations.

Note: Similar to Katana’s CEL, USD’s Pattern-Based Collections (PBC) was introduced in USD 23.11 and is now fully integrated in Katana’s USD framework, with the addition of a Pattern-Based Collection (PBC) widget and the UsdCollection node, available as of Katana 7.5. See Pattern-Based Collections with USD.

You can see a list of the CEL and USD (PBC) Collections in your project in the Collections panel at the top of the Scene Explorer and via the Collection working set indicators . See Using the Scene Explorer.