xephyr:tldr:a33dc

This command runs the Xephyr X server with specific options:

• -br stands for "backing-store" and instructs Xephyr to enable backing store support. Backing store is a feature that allows programs to remember the contents of windows even when they are not currently visible.
• -ac stands for "access control" and disables access control restrictions, allowing connections from any host.
• -noreset prevents the Xephyr server from resetting the server on startup.
• -screen ${800x600} sets the screen resolution for Xephyr to 800x600 pixels.
• ${:2} is a variable that represents the display number on which Xephyr server will run. The display number is usually a two-digit number starting from ":0", ":1", and so on.

When this command is executed, it starts the Xephyr X server with the specified options and creates a nested X11 server within a window of the host X server. The screen resolution is set to 800x600 pixels, and it allows connections from any host.