Static string in DwCA query?

How do I include a static string in my query to export data via the RSS feed?

I’m hoping that it’s something close to what I have guessed below (highlighted part), where I want to insert microliters statically because I don’t have a field containing the unit of DNA concentration:

Yes, you can add a static string or default value by including it in the value= string. However, be aware that some aggregators do not accept static strings and cannot parse them. I can’t remember who it was that was complaining about them. The alternative is to add that value to a higher table like collection or institution and map that field to the DwC concept instead as a constant.

<field term="http://rs.tdwg.org/dwc/terms/institutionCode" value="KU"/>

Thanks Andy - very useful.