This is part of CLPR#3403

In T800#11838, @nrwahl2 wrote:

<define name="non-empty-string">
   <data type="string">
      <except><value></value></except>
   </data>
</define>

It turns out that due to the same normalization you described, any value that consists of only spaces is rejected. Not just empty strings.

Which might be fine for our purposes, but we need to be aware of it.

For this task, we only need a deprecation warning. When we get around to dropping support for master, the code won't have to worry about it at all -- an XSL transform will map master to clone before the code ever sees it.

Taking a look at crm_map_element_name...