System plugins operate every time a page on your site loads. They control such things as your URLS, whether users can check a "remember me" box on the login module, and whether caching is enabled.  New in 1.6 is the redirect plugin that with the redirect component assist you in managing changes in URLs.
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Content plugins run when specific kinds of pages are loaded. They do things ranging from protecting email addresses from harvesters to creating page breaks.
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Two new plugins are available in 1.6 but are disabled by default.
Cannot get Irvine location id in module mod_sp_weather. Please also make sure that you have inserted city name.