Facebook launched a new plugin for webpages, which allows people to send a private message to a person, group or email address.
Facebook's dev blog says this about the new feature:
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"The send dialog is better than the dend button for deep integrations because it enables developers to build sending messages into the core flow of their website or app… The new dialog was designed for activities that a user may want to only share with specific people, which makes it particularly useful for ecommerce, travel, and event websites…. Facebook messages are intended for high quality conversations between friends, not impersonal, unwanted messages. Apps on Facebook should use requests to let people communicate in-game status, invite friends to use an app, or send messages to multiple people. The send dialog is appropriate when a person might otherwise send a personal email."