Note: This is a request that a previously declined feature be reconsidered based on the below arguments. If this is not a proper use of the feature request system, feel free to downvote/remove this request.  

What functionality is missing? What is unsatisfying with the current situation?

The lack of variables in manuscripts is a point of frustration for fictional work authors who are looking to share their works with friends, family, and users who are unfamiliar with using WorldAnvil as a platform. The lack of this feature does not change how authors write, instead it forces them to add a clunkier reference system (such as a traditional glossary section) or move to another platform to host their works. WorldAnvil's manuscript system already includes a variety of multimedia support options, including links, images, and audio attachments. Variables would not be a far extension from the features and options already made available to authors.  

How does this feature request address the current situation?

The ability to add variables (as a form of general tooltips) into manuscripts, while likely making said manuscript non-exportable (or at least difficult to export without editing), would be a useful feature implementation not just for writers, but more specifically for readers of manuscripts and written works that are hosted exclusively on WorldAnvil.   While plenty of manuscripts are used for drafting, atlas, or other purposes that would not feasibly benefit from this feature (likely making it a low priority even if reconsidered), there are a significant portion of manuscripts that are made specifically as original and/or fan works. WorldAnvil's manuscript publishing system is a well-made service that can already host these fan works to be shared. This is especially beneficial for authors who may not want to go through the effort of setting up a WordPress or AO3 account to publish their works through. Likewise, additional UI and QOL implementations, while presenting complications for exporting, would still be a useful even if niche feature for authors who want to self-host their works on WorldAnvil and share them with users who may not be familiar with the site's overall UI.   Uses of similar Variable style systems in writing can be found not only in web serials and other forms of written media (a great example is the Owlcat series of CRPGs), but similar versions can be found in real world published works, especially fiction and fantasy works. Variables are functionally a footnote or glossary system with an improved UI thanks to being hosted on a webpage and not paper. The alternative to variable implementation in a manuscript that would benefit from it would be footnotes or a glossary, which at that point would functionally just be a workaround to get past a missing feature.  

What are other uses for this feature request?

Beyond merely fictional works, Variables may benefit other Manuscript users as well, offering a way of storing in-line notes or citations, or for summarizing reference materials. The only people it would be a problem for are users who intend to export their work outside of WorldAnvil, who could simply choose not to use the system to prevent this issue. It is worth considering that several features Manuscript offers already would complicate exporting the work, such as links and audio support.   On the basis of the above points, I humbly request the WorldAnvil team reconsider this as a feature for future Manuscript updates.