the encapsulated
        triangulation from its border-located flat triangles
        (according to their :meth:`circle_ratios`).
        This mask is meant to be subsequently applied to the triangulation
        using `.Triangulation.set_mask`.
        *new_mask* is an extension of the initial triangulation mask
        in the sense that an initially masked triangle will remain masked.

        The *new_mask* array is computed recursively; at each step flat
        triangles are removed only if they share a side with the current mesh
        border. Thus, no new holes in the triangulated domain will be created.

        Parameters
        ----------
        min_circle_ratio : float, default: 0.01
            Border triangles with incircle/circumcircle radii ratio r/R will
            be removed if r/R < *min_circle_ratio*.
        rescale : bool, default: True
            If True, first, internally rescale (based on `scale_factors`) so
            that the (unmasked) triangles fit exactly inside a unit square
            mesh.  This rescaling accounts for the difference of scale which
            might exist between the 2 axis.

        Returns
        -------
        array of bool
            Mask to apply to encapsulated triangulation.
            All the initially masked triangles remain masked in the
            *new_mask*.

        Notes
        -----
        The rationale behind this function is that a Delaunay
        triangulation - of an unstructured set of points - sometimes contains
        almost flat triangles at its border, leading to artifacts in plots
        (especially for high-resolution contouring).
        Masked with computed *new_mask*, the encapsulated
        triangulation would contain no more unmasked border triangles
        with a circle ratio below *min_circle_ratio*, thus improving the
        mesh quality for subsequent plots or interpolation.
        r