Availability:built-in
string, number
or
bool. String results are returned as an atom, number
results as an integer, and bool results as the atom on or off.
If an option cannot be found, this predicate fails silently. The results
are only computed once. Successive queries on the same capability are
fast. This predicate can raise several exceptions if the terminal
environment is incomplete, notably if the environment variable TERM
does not exist or there is no matching entry in the termcap database.