bmesh1=ToBoundaryMesh[Rectangle[],"MaxBoundaryCellMeasure"Infinity];bmesh2=ToBoundaryMesh["Coordinates"{{1/4,1/2},{2/3,1/2}},"BoundaryElements"{LineElement[{{1,2}}]}];bmesh3=ToBoundaryMesh[Rectangle[{2/3,1/3},{4/5,2/3}],"MaxBoundaryCellMeasure"Infinity];