Some pages shouldn't be indexed by search engines.  For example, any print version of a page, and any login page, and any page whose content varies so frequently that searching an index of it would yeild an out-of-date, irrelevant link.   For these pages, the following search engine-disabling metatag is appropriate (we have employed it on various Presto pages, including the default print template.):

<META NAME="robots" CONTENT="noindex,nofollow,noarchive">

More documentation about this is available at: http://www.google.com/bot.html#noindextags .

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