Select Boundaries selects the bounding entities of the currently selected entities. Please refer to the figure below for a complete listing of entity to bounding entity relationships. Note that for grid entities, Select Boundaries gives the same results as Select Parents when using the Standard hierarchy mode.
Tip: For models, Select Boundaries selects any lamina edges that are present within the model. This can be helpful in locating small gaps that need to be closed using Assemble Models.
