A matrix representing the interactions observed between higher trophic level species (columns) and lower trophic level species (rows). Usually this will be number of pollinators on each species of plants or number of parasitoids on each species of prey.

sort.order can be either
inc: sorted by increasing row/column totals
dec: sorted by decreasing row/column totals
seq: sorted by a given order, see sequence for how to specify an order

list of two with two named vectors: seq.lower and seq.higher, which specify the order in which species are sorted. To be able to sort by names obviously the given web must be a NAMED matrix, i.e. has column and row names. If you want to order an unnamed web, you can either order it by row/column totals are you have to simply specify the sequence as follows (example puts last row/column to the front): web[c(9, 1:8), c(27, 1:26)]