Report the terminal window title.
The terminal replies:
ESC]lⓈESC\
Where data usually is the empty string, because this control sequence turned out to be a security hazard.
If explicitly enabled by the user of the terminal some implementations report the window title in data. If enabled with set title mode the string is hex encoded.
🛆 urxvt always uses ST as terminator instead of ESC\.
Source explains:
Report a static window title, since the real window title should NEVER be reported, as it creates a security vulnerability. See http://marc.info/?l=bugtraq&m=104612710031920&w=2 and CVE-2003-0070.