"5.10.0 (AS1004)" is BrowerUK's shorthand for "ActivePerl 5.10.0, build 1004".

 Perl major version
      --
      1004
        --
    build number of
   that Perl version
[download]

It's ActiveState's 4th or 5th build of Perl 5.10. It happens to be a build of 5.10.0, but the minor version isn't specified by the build number.

1006 was their first build of 5.10.1.