(Incomplete) list of special symbols:

comparison:  = != < > <= >= not matches contains
boolean:     ! & | -> (...) [...]
regexp:      ? * + {..} | (...)
query:       :: ;
file i/o:    > < >>
variables:   = < += -=
misc:        .. ... 
escape:	     `



List of reserved tokens (must not be used for attributes, built-in functions, ...)

asc
ascending
by
cat
cd
collocate
contains
cut
def
define
delete
desc
descending
diff
difference
discard
dump
exclusive
exit
expand
farthest
foreach
group
host
inclusive
info
inter
intersect
intersection
join
keyword
left
leftmost
macro
maximal
match
matchend
matches
meet
MU
nearest
no
not
NULL
off
on
randomize
reduce
RE
reverse
right
rightmost
save
set
show
size
sleep
sort
source
subset
TAB
tabulate
target
target0 ... target9
to
union
unlock
user
where
with
within
without
yes
