A *``required``* relationship \ .\ ``relationship``\ .\  ``dir1:from_to`` \ .\ ``entity``\ .\  ``dir2:from_to`` \ .\ ``other_entity``\ .\ 
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Usages:
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 - **Then** *a *required* relationship .IfcRelContainedInSpatialStructure. to .IfcElement. from .IfcSpatialStructureElement.*

   :doc:`/features/SPS007_Spatial-containment`:29