Basic Idea:

  slrn awards an article points by giving it a score.  If the score for the
article is less than zero, the article is marked as read or killed.  The
purpose of the score file is to define the set of tests that an article must
go through to determine the score.  Although the score may be based on ANY
header item, it is recommended that one stick with the following for
efficiency:

      * Subject
      * From
      * Xref
      * References
      * Lines
      
as well as the newsgroup that the article is part of.
  
Score file format:

  The format of the file is very simple (See below for an explicit
example). The file is divided into sections delimited by a newsgroup
or newsgroups enclosed in square brackets, e.g.,

     [rec.crafts.*, rec.hobbies.*]

The name may contain the `*' wild card character.  

Comments begin with the `%' character.  Leading whitespace is ignored.

Each section consists of comment lines, empty lines or keyword lines.
Only the keyword lines are meaningful and all leading whitespace is
ignored.  A keyword line begins with the name of the keyword followed
immediately by one or two colons and one space.  The rest of the line
usually consists of a regular expression.  The keyword may be prefixed
by the `~' character to signify that the regular expression should not
match the object specified by the keyword.

A group of keywords defines a test that is given to the header of the
article.  The `Score' keyword is used to assign a score to the header
if the header passes the test.  It also serves to delimit tests.  The
score can be any positive or negative integer.  However there are two
special values: 9999 and -9999.  If the score for an individual test
is one of these two values, any following tests are skipped and the
article is simply given one of the two special values.  If the
numerical value of the score is prefixed by an equal sign, score
processing for the header is stoped and the header will be given the
score for that test.

All keywords except for `Score' and `Expires' may be prefixed by the `~'
character.  If the `Expires' keyword appears, it must immediately follow the
`Score' keyword.  The `Expires' keyword may be used to indicate that the
test is no longer to be applied on the date specified by the keyword.  For
example,

    Expires: 4/1/1996              (or: 1-4-1996)

implies that the given test is no longer valid on or after April first 1996.
As the example indicates, the date must be specified using either the format
MM/DD/YYYY or DD-MM-YYYY.  Note: DO NOT CONFUSE THIS WITH THE EXPIRES HEADER
KEYWORD.

The Lines keyword is also special.  Its value is not a regular expression,
rather, a simple integer.  It may be used to kill articles which contain too
many or too few lines.  For example,

    Score: -100
    Lines: 1000
    
assignes a score of -100 to articles that have more than 1000 lines.
Similarly, the test

    Score: -100
    ~Lines: 3
    
assigns a score to articles that have less than or equal to 3 lines.

Here is a sample slrn score file:
-------------------------------------------------------------  
  [news.software.readers]
     Score: 9999
     % All slrn articles are good
     Subject: slrn
  
     Score: 9999
     % This is someone I want to hear from
     From: davis@space\.mit\.edu

     Score: -9999
     Subject: \<f?agent\>

  [comp.os.linux.*]
     Score: -10
     Expires: 1/1/1996
     Subject: swap
     
     Score: 20
     Subject: SunOS
      
     Score: 50
     From: Linus
     
     % Kill all articles cross posted to an advocacy group
     Score: -9999
     Xref: advocacy
     ~From: Linus
     
     % This person I want nothing to do with unless he posts about 
     % `gizmos' but only in comp.os.linux.development.*
     
     Score: -9999
     From: someone@who\.knows\.where
     ~Subject: gizmo
     ~Newsgroup: development
  
  [~misc.invest.*, misc.taxes]
     Score:: -9999
      Subject: Earn Money
      Subject: Earn \$
      
--------------------------------------------------------  

This file consists of two sections.  The first section defines a set
of tests applied to the news.software.readers newsgroups.  The second
section applies to the comp.os.linux newsgroups. The final section
applies to ALL newsgroups EXCEPT misc.invest.* and misc.taxes (see
below).

The first section consists of three tests.  The first test applies a score
of 9999 to any subject that contains the string `slrn'.  The second test
applies to the `From'.  It says that any article from davis@space.mit.edu
gets scores 9999.  The third test gives a score of -9999 to any article
whose subject contains the word `agent'.  Since tests are applied in order,
if an article contains both `slrn' and `agent', it will be given a score of
9999 since 9999 is a special score value.

The second section is more complex.  It applies to the newsgroups
comp.os.linux newsgroups and consists of 5 tests.  The first three are
simple: -10 points are given if the subject contains `swap', 20 if it
contains SunOS, and 50 if the article is from someone named `Linus'.  This
means that if Bill@Somewhere writes an article whose subject is `Swap, Swap,
Swap', the article is give -10 points.  However, if the Linus writes an
article with the same title, it is given -10 + 50 = 40 points.  Note that
the first test expires at the beginning of 1996.

The fourth test kills all articles that were cross posted to an advocay
newsgroup UNLESS they were posted by Linus.  Note that if a keyword begins
with the `~' character, the effect of the regular expression is reversed.

The fifth test serves to filter out posts from someone@who.knows.where
unless he posts about `gizmos' in one of the comp.os.development newsgroups.
Again note the `~' character.

The final section of the score file begins with the line

  [~ misc.invest.*, misc.taxes]

If the first chaarcter following the opening square bracket is `~',
then the newsgroup or newsgroups contained in the brackets are NOT to
be matched.  That is, the `~' character is used to denote the boolean
NOT operation.
