The Word Processor Nota Bene has a feature which I would like if possible to emulate within Emacs. One can insert into a document non-printing markers which are then used to delineate areas of text or individual keywords to be indexed in text files. For example in the paragraph below the area in double brackets would be the area that would be searched in a document, as opposed to the whole document.
[[Emacs is the extensible]], customizable, self-documenting real-time display editor. This manual describes how to edit with Emacs and some of the ways to customize it; it corresponds to GNU Emacs version 26.3.
If one then did a search through the Nota Bene search tool Orbis, one would search for (say) the word "extensible" and only the text between the markers would be searched. This allows one to more easily find specific information in a file, rather than having to search through dozens of possible hits.