BOF consists of a 'Leader' within which an 'ISO/IEC 8211 Record Identifier', 'Data Set Identification field' (DSID), and 'Data Set Structure information field' (DSSI) are found. This is followed by a 'DR Leader' containing values defined in the DSID, including the S-57 format 'Edition' value.
For the purposes of an identification signature, we're seeking from offset 5 "3LE1 09" {0-2048} "ISO/IEC 8211 Record Identifier" {0-128} "Data set identification field" {0-512} "STED!" {0-4096} 0x1E {5} " D " {16-256} "03.1"