Selects the area for which the **condif_convection** record with
the same *index* should be applied.
This is only available for linear elements.

In 1D, the convective heat flux is 0.
In 2D this option is available for all elements.
In 3D this option is only available for all linear elements.
In stead of a number of nodes also,
by example, **-geometry_line 1** can be used in 2D, indicating that
the nodes on line 1 start to convect.
See also: **condif_convection**.

tochnog 2001-09-02