Modes: a q s
EXTERNAL uses an external application to retrieve sequences. The ID is passed as an argument to the application, either replacing %s in the command string (if present) or as an additional arguement (if there is no %s). EXTERNAL expects the application to return the sequence on STDOUT.
DB mydb [
#required parameters
method: app
format: fasta
app: "getfromdb mydb"
#optional parameters
type: P
comment: "my own protein database with a custom retrieval program"
]