-<P>All filters work in basically the same way. There are several elements delimited by commas. I will use the spot filter as an example ....
-<P>
-<P>The elements of the Spot filter are ....
-<P>
-<BLOCKQUOTE><CODE>
-<PRE>
-[action, field_no, sort, possible_values, hops]
-</PRE>
-</CODE></BLOCKQUOTE>
-<P>
-<P>There are 3 elements here to look at. Firstly, the action element. This is very simple and only 2 possible states exist, accept (1) or drop (0).
-<P>
-<P>The second element is the field_no. There are 13 possiblities to choose from here ....
-<P>
-<BLOCKQUOTE><CODE>
-<PRE>
- 0 = frequency
- 1 = call
- 2 = date in unix format
- 3 = comment
- 4 = spotter
- 5 = spotted dxcc country
- 6 = spotter's dxcc country
- 7 = origin
- 8 = spotted itu
- 9 = spotted cq
- 10 = spotter's itu
- 11 = spotter's cq
- 12 = callsign of the channel on which the spot has appeared
-</PRE>
-</CODE></BLOCKQUOTE>
-<P>
-<P>The third element tells us what to expect in the fourth element. There are 4 possibilities ....
-<P>
-<BLOCKQUOTE><CODE>
-<PRE>
- n - numeric list of numbers e.g. [ 1,2,3 ]
- r - ranges of pairs of numbers e.g. between 2 and 4 or 10 to 17 - [ 2,4, 10,17 ]
- a - an alphanumeric regex
- d - the default rule
-</PRE>
-</CODE></BLOCKQUOTE>
-<P>
-<P>The fifth element is simply the hops to set in this filter. This would only be used if the filter was for a node of course and overrides the hop count in hop_table.pl.
-<P>
-<P>So, let's look at an example spot filter. It does not matter in the example who the filter is to be used for.
-So, what do we need in the filter? We need to filter the spots the user/node requires and also set a default rule for anything else outside the filter. Below is a simple filter that stops spots arriving from outside Europe.
-<P>
-<BLOCKQUOTE><CODE>
-<PRE>
-$in = [
- [ 0, 4, 'a', '^(K|N|A|W|VE|VA|J)'], # 0 = drop, 'a' = alphanumeric
- [ 1, 0, 'd', 0, 1 ], # 1 = want, 'd' = everything else
- ];
-</PRE>
-</CODE></BLOCKQUOTE>
-<P>
-<P>So the filter is wrapped in between a pair of square brackets. This tells Spider to look in between these limits. Then each line is contained within its own square brackets and ends with a comma.
-Lets look carefully at the first line. The first element is 0 (drop). Therefore anything we put on this line will not be accepted. The next element is 4. This means we are filtering by the spotter. The third element is the letter "a" which tells the program to expect an alphanumeric expression in the fourth element. The fourth element is a list of letters separated by the pipe symbol.
-<P>
-<P>What this line does is tell the program to drop any spots posted by anyone in the USA, Canada or Japan.