A compose sequence is a combination of two keys pressed sequentially to create a special character not available on the keyboard. Using compose sequences, you can enter special characters on a VT terminal screen.
Compose sequences work only in Compose (CMP) mode. When you start Compose mode, the CMP indicator appears in the status line. Some compose sequences are available when you use both the ISO Latin-1 or DEC Supplemental UPS (User-Preferred Supplemental) character set; other compose sequences are available to specific character sets.