+used_by vim
+userdef BD str - disables bracketed paste
+userdef BE str - enables bracketed paste
+userdef PE str - is sent after pasted text
+userdef PS str - is sent before pasted text
+userdef RV str - report terminal secondary device attributes
+userdef XR str - report terminal version as a free-format string.
+userdef XF bool - terminal supports xterm focus in/out
+userdef rv str - response to RV, regular expression
+userdef xr str - response to XR, regular expression
+#