+ \item{as.matrix}{(used if \code{format = "fasta"}) one of the three
+ followings: (i) \code{NULL}: returns the sequences in a matrix if
+ they are of the same length, otherwise in a list; (ii) \code{TRUE}:
+ returns the sequences in a matrix, or stops with an error if they
+ are of different lengths; (iii) \code{FALSE}: always returns the
+ sequences in a list.}