get the window class

xprop | awk '
	/^WM_CLASS/{sub(/.* =/, "instance:"); sub(/,/, "\nclass:"); print}
	/^WM_NAME/{sub(/.* =/, "title:"); print}'

output:

instance: "Navigator"
class: "Firefox"
title: "Mozilla Firefox

dwm specified some windows to specified tag

if the some apps have tow windows, each windows should specified the class and instance and title, that help dwm to disting between windows

static const Rule rules[] = {
    /* class       instance      title           tags_mask isfloating   monitor */
    { "Firefox",   "Toolkit",   "Picture-in-Picture", 1 << 4,   0, -1 },
    { "Firefox",   "Navigator", "Mozilla Firefox",    1 << 3,   0, -1 },
}