How to use watch in gruntjs to assign multiple tasks to multiple files

I'm trying to do this (pseudo code):

watch

files: fileset1 (for example: *.less), fileset2 (for example: *.mustache)
tasks: 'less','rake'

Is it possible? If so, how?

Taken from the Grunt jQuery example:

watch: {
   files: ['*.less', '*.mustache'],
   tasks: 'less rake'
}