The -dita-use-conref-target attribute value

A special attribute value of -dita-use-conref-target can be used to force the attribute value of the source of a conref to be used in the referencing element.

The attributes on some DITA elements are mandatory, such as the trademark type (tmtype) attribute of a trademark (tm) element. When you conref such an element, the source element's attributes are not ascribed to the referencing element. The referencing conref element is therefore invalid, because it lacks the mandatory attribute.

For example, the trademark element:
<tm id="tm_hyperwrite" tmtype="reg">HyperWrite</tm>
would logically be referenced using conref as:
<tm conref="#about_company/tm_hyperwrite"/>
However, because that referencing tm element does not include a tmtype attribute, it is invalid.
To circumvent the invalidity, you could also include the attribute in the referencing element, as:
<tm conref="#about_company/tm_hyperwrite" tmtype="reg"/>

However, this involves repeating the same information, which goes against the ideal of re-using rather than copying.

DITA elements that have mandatory attributes, or that have enumerated values (that is, a fixed choice of valid values), also have a -dita-use-conref-target value. This value forces the attribute value of the conref source (the referenced element) being used in the referencing element.

A conref to a trademark could therefore be coded as:
<tm conref="#about_company/tm_hyperwrite" tmtype="-dita-use-conref-target"/>