Is it possible to add custom attributes in Microdata?

Question

Is there an option to add custom attributes to a scheme? (same as we can expand DTD?)

itemprop="description" isn't enough for me. I got more attributes that I wish to add, that do not exist in the original scheme:

I need this attributes cause they project the full characteristic of my product.

possible duplicate of [Schema.org: How to extend a class](http://stackoverflow.com/questions/27581209/schema-org-how-to-extend-a-class) — neoswf, Mar 05 '15 at 17:37
Which does not have a satisfactory answer... It basically says 'just don't extend but use these existing properties' — Stijn de Witt, Jul 06 '17 at 11:06

score 1 · Accepted Answer · edited May 23 '17 at 11:56

In Microdata, you can use a "proprietary item property name":

one used by the author for private purposes, not defined in a public specification

It has to be an absolute URL, e.g.:

<div itemscope itemtype="http://schema.org/Thing">
  <p itemprop="description">…</p>
  <p itemprop="http://example.com/voc/objective">…</p>
</div>

(Of course you can’t expect other consumers to make use of it.)

If you are using the Schema.org vocabulary, you could also:

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