When published as HTML, sometimes multiple rendered documents will appear on the same page, such as on a blog that displays the full text of multiple posts on its home page. If the sources use identical footnote labels (e.g. [^1], [^2], etc.), then the anchors for the reference links and backlinks will collide when they are displayed on the same page.

Not every project will be affected by this. But for those that are, could we add a new parameter named, e.g., footnote-label-prefix, defaulting to "", and prefix its value to all footnote labels in the document during parsing?

#lang racket/base

(require commonmark racket/file)

(define (my-post-renderer source-file)
  (define source-str (file->string source-file)
  (parameterize ([footnote-label-prefix (my-unique-id-maker source-file)])
    (document->html (string->document source-str))))

If you are not interested, please feel free to close this issue without comment. I understand it’s an edge case, and it’s already possible to avoid this by taking care to use reasonably unique labels when writing the markdown source. Also, I could always traverse the AST after the parse and prefix all the labels before rendering. I just thought I’d ask, since it would be faster and more ergonomic to handle it during at parse time.