Mixed-Dimension Meshes 

Meshes can contain components of any dimension up to their embedding dimension.

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X mesh2d = MeshRegion[{{0, 0}, {1, 0}, {2, 0}, {3, -1/2}, {3, 1/2}}, {Point[{1}], Line[{2, 3}], Triangle[{3, 4, 5}]}]

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The components can be separated out, based on dimension.

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X DimensionalMeshComponents[mesh2d]

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A mixed-dimensional mesh in 3D.

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X MeshRegion[{{0, 0, 0}, {1, 0, 0}, {2, 0, 0}, {3, 0, 1/2}, {3, 0, -1/2}, {4, 1/2, 0}, {4, -1/2, 0}}, {Simplex[{1}], Simplex[{2, 3}], Simplex[{3, 4, 5}], Simplex[{4, 5, 6, 7}]}]

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