Remove extraneous DOCTYPE
Move script to the end of the document so it will be loaded after the document is rendered
It would be helpful to load jQuery
Since this file is being run locally, protocol is needed for jQuery URL
Add basic structure for a jQuery plugin, as shown at http://learn.jquery.com/plugins/basic-plugin-creation/
Blink function working for the first case (speed = 1000)
Adding missing semicolon caught by jshint
Add a second <div> to test another value for blink speed
Add one more test, to check that the plugin properly supports chaining (another jQuery method can be called on the value the plugin returns)