def _write_entities(fh, cells, binary):
    """write the $Entities block

    specified as

    numPoints(size_t) numCurves(size_t)
      numSurfaces(size_t) numVolumes(size_t)
    pointTag(int) X(double) Y(double) Z(double)
      numPhysicalTags(size_t) physicalTag(int) ...
    ...
    curveTag(int) minX(double) minY(double) minZ(double)
      maxX(double) maxY(double) maxZ(double)
      numPhysicalTags(size_t) physicalTag(int) ...
      numBoundingPoints(size_t) pointTag(int) ...
    ...
    surfaceTag(int) minX(double) minY(double) minZ(double)
      maxX(double) maxY(double) maxZ(double)
      numPhysicalTags(size_t) physicalTag(int) ...
      numBoundingCurves(size_t) curveTag(int) ...
    ...
    volumeTag(int) minX(double) minY(double) minZ(double)
      maxX(double) maxY(double) maxZ(double)
      numPhysicalTags(size_t) physicalTag(int) ...
      numBoundngSurfaces(size_t) surfaceTag(int) ...
    ...

    """
    return
