schema.org - Can I add a tag within a tag in Microdata? -

i in process of tagging content forthcoming training course. sort of getting hang of it. have description:

<span itemprop="description">this 2 day certificated course meets requirements of management standards ....</span> 

but declare duration of course. question can within tag?

so instead have:

 <span itemprop="description">this <span itemprop="duration">2 day</span> certificated course meets requirements of management standards ....</span> 

or confuse google (etc.)?

this fine (except value of duration property, should "in iso 8601 date format").

every conforming microdata parser extract following values:

• description:

  this 2 day certificated course meets requirements of management standards ....

• duration:

  2 day