Pragmatic Modules
    They work somewhat like compiler directives (pragmata) in that they tend
    to affect the compilation of your program, and thus will usually work well
    only when used within a "use", or "no". Most of these are lexically
    scoped, so an inner BLOCK may countermand them by saying:

        no integer;
        no strict 'refs';
        no warnings;

    which lasts until the end of that BLOCK.

    Some pragmas are lexically scoped--typically those that affect the $^H
    hints variable. Others affect the current package instead, like "use vars"
    and "use subs", which allow you to predeclare a variables or subroutines
    within a particular file rather than just a block. Such declarations are
    effective for the entire file for which they were declared. You cannot
    rescind them with "no vars" or "no subs".

  Standard Modules
    Standard, bundled modules are all expected to behave in a well-defined
    manner with respect to namespace pollution because they use the Exporter
    module. See their own documentation for details.

    To find out all modules installed on your system, including those without
    documentation or outside the standard release, just use the following
    command (under the default win32 shell, double quotes should be used
    instead of single quotes).

        % perl -MFile::Find=find -MFile::Spec::Functions -Tlwe \
          'find { wanted => sub { print canonpath $_ if /\.pm\z/ },
          no_chdir => 1 }, @INC'

    (The -T is here to prevent '.' from being listed in @INC.) They should all
    have their own documentation installed and accessible via your system
    man(1) command. 

    Note also that the command "perldoc perllocal" gives you a (possibly
    incomplete) list of the modules that have been further installed on your
    system. (The perllocal.pod file is updated by the standard MakeMaker
    install process.)

  Extension Modules
    Extension modules are written in C (or a mix of Perl and C). They are
    usually dynamically loaded into Perl if and when you need them, but may
    also be linked in statically. Supported extension modules include Socket,
    Fcntl, and POSIX.

    Many popular C extension modules do not come bundled (at least, not
    completely) due to their sizes, volatility, or simply lack of time for
    adequate testing and configuration across the multitude of platforms on
    which Perl was beta-tested. You are encouraged to look for them on CPAN
    (described below), or using web search engines like Alta Vista or Google.