Adding indepentently resizable symbols into your custom shapes is possible by creating subshapes. This is done by some extra attributes on the group element.
<svg:g
dia:subshape="true"
dia:v_anchor="fixed.bottom"
dia:h_anchor="fixed.left"
dia:default_scale="1.0">
-
dia:v_anchor[Definition: Supported values:
"fixed.top""fixed.bottom""proportional"] - The vertical anchoring of the subshape.
-
dia:h_anchor
[Definition: Supported values are:
"fixed.left""fixed.right""proportional"] - The horizontal anchoring of the subshape.
- dia:default_scale
- currently unused