The key (destination) should be an unique filepath (supports [grunt.template](https://github.com/gruntjs/grunt/blob/master/docs/api_template.md)) and the value (source) should be a filepath or an array of filepaths (supports [minimatch](https://github.com/isaacs/minimatch)).
This option accepts a function which takes one argument (the template filepath) and returns a string which will be used as the key for the precompiled template object. The example below stores all templates on the default JST namespace in capital letters.