Explanation about maxspan, maxgap, and mingap can be found in Chapter 7.4.3
in the course book. 

The above quantities are additional constraints that can be used to restrict
the mining of sequential patterns. 

The maxspan constraint specifies the maximum allowed time difference between
the latest and the earliest occurrences of events in the entire sequence.
Suppose we have a sequential pattern p = <{a} {b}> then for maxspan = 2 the
data sequence <{a} {c} {b}> supports p, but the data sequence 
<{a} {c} {d} {b}> does not. 

The maxgap and mingap constraints define upper and lower bounds, respectively,
for the time difference between two consecutive elements of a sequence.
maxgap is similar to maxspan, but requires consecutive elements of a sequence
to be within maxgap time instances. mingap puts a lower bound on the same time
period and requires the time period to be at least mingap time instances long.
For an example see the bottom table on page 437.

Note that the min/maxgap constraints might violate the Aprioi-principle, i.e.
it is possible that for a sequence dataset 
supp(<{a} {b} {c}>) > supp(<{a} {c}>)!