New Post: Show in detail.html new product fields

I added new product fields to the productfields.html theme.

[<tag id="productfields" type="postback" value="" />]
[<tag id="localizedproductfields" type="postback" value="genxml/textbox/urlcompra" />]
<div class="col-sm-12"><label class="control-label">URL Compra:</label>[<tag type="editflag" />] [<tag id="urlcompra" cssclass="form-control" type="textbox" maxlength="250" />]</div> The textbox is showing correctly in the Products BackOffice.
But how can I add this fields content to the "detail.html" template??
Adding [<tag type="urlcompra" />] doesn´t show me anything...

Thank you.