The <application>rxvt-unicode</application> terminal emulator uses the resource class <classname>URxvt</classname> and the resource name <classname>urxvt</classname>. You can add X resource definitions to a user's <filename>~/.Xresources</filename> or <filename>~/.Xdefaults</filename> files or to the system-wide <filename>/etc/X11/app-defaults/URxvt</filename> file. The following example will load the <classname>matcher</classname><application>Perl</application> extension (assuming <application>Perl</application> support wasn't disabled), which enables a left button click to open an underlined URL in the specified browser, sets a background and foreground color and loads an Xft font (as the <systemitem class="username">root</systemitem> user):