This signal is emmitted whenever the size of the panel the plugin is on changes.
Plugins writers can for example use this signal to update their icon size.
If the function returns false or is not used, the panel will force a square size to the plugin. If you want non-square plugins and you don't need this signal you can use something like this:
g_signal_connect (plugin, "size-changed", G_CALLBACK (gtk_true), NULL);
| size |
the new size of the panel. |