Here is an instruction for developers which describes how it is possible to add children Regions into custom Region plug-in:
ChildrenRegions.pdf (187 KiB) downloaded 67 time(s).

Andrey,

Word wrap in text regions is great!
The new children mechanism seems to provide a lot of options. First of all I think of plot regions with axis limits and expressions being handled much like in Mathcad.

An interesting option is to provide language-specific definitions, as the contents of a text region including all children can be language-specific. In the past I did this in the Maxima-Plugin-Test using the value of math region descriptions. In fact, you can provide localized definitions by putting math regions inside otherwise empty text regions.

Martin

Wrote

First of all I think of plot regions with axis limits and expressions being handled much like in Mathcad.

You mean as a new 2D plugin, that will plot crappy traces
as crappy as Mathacd caused by imposed limits, whereas it
won't plot on pixels anymore. Mathcad plots on ½ pica.
and can about never plot 2 plots of equal height/width.
Argument style is debatable. Older SS does not open
most latest versions. Good idea to relax the old wolf
from reading same paper [same Smath document] as the youngest ones.
Smath handles the X, Y directions by pixels,
Mathcad handles in ½ pica.