In this case, the output would likely just be used as a string replacement for the macro invocation. The downside of allowing this would be the ability to create "write-only" (non-human readable) nimble files. I am honestly kinda okay with that :)

#macro linkable
  #arg title nimble Missing Title
  #arg slug raw missing-title
  #result nimble
    #raw html <a id="{{slug}}" style="visibility: hidden; position: relative; top: -40px; width: 0px; height: 0px; z-index: -32767; border: 0px; margin: 0px; padding: 0px;"></a>
    { {{title}}

In this case, the output could still just be used as a string replacement for the macro invocation. However, if the result is rendered to the output format first, then this could restrict the writer from creating anything too chaotic as to be unreadable from the nimbe source alone.

#macro linkable
  #arg title nimble Missing Title
  #arg slug raw missing-title
  #arg content nimble missing content.
  #result nimble
    #raw html <a id="{{slug}}" style="visibility: hidden; position: relative; top: -40px; width: 0px; height: 0px; z-index: -32767; border: 0px; margin: 0px; padding: 0px;"></a>
    { {{title}}
    {{content}}
    }

Related to Nimble Macros with nimble output, Having a library of common macros would be nice.

Currently I just do one of these:

• #raw html <!-- This is a comment that also shows up in the output. -->
• #raw comment This is a comment only visible in nimble. But easily filterable.
• #raw This is a comment only visible in nimble.

This is a bit odd and not quite as easy as most other languages. Though I could maybe see a use-case for something like #raw disabled vs #raw comment or #raw TODO if it meant you could interact with these lines differently with tooling.

Both for IDEs to have any support for the language, and also mechanisms for Nimble code blocks to be styled in HTML based on language.