For a long while, I thought you should add things like "_NET_WM_WINDOW_TYPE_DIALOG", the literal output of xprop/obxprop, but you should actually just abbreviate this part at least to either
"normal, dialog, splash, utility, menu, toolbar, x, or desktop", as the comment-description that should come in the default rc.xml says.
That's particularly useful if you have different rules for different windows of the same application, like having the main window maximized...