On 13/02/2021 11:38, Kyle Meyer wrote: > > +(defun org--open-file-format-spec (format specification) > + (with-temp-buffer > + (insert format) > + (goto-char (point-min)) > + (while (search-forward "%" nil t) > + (cond ((eq (char-after) ?%) > + (delete-char 1)) > + ((looking-at "[s0-9]") > + (replace-match > + (or (cdr (assoc (match-string 0) specification)) > + (error "Invalid format string")) > + 'fixed-case 'literal) > + (delete-region (1- (match-beginning 0)) (match-beginning 0))) Finally I managed to convince myself that delete-region does not change position in the buffer, so "%s" or "%1" in specification are not a problem. I am aware that this implementation is a simplified version of format-spec, but I am still unsure if jumping over a buffer is the best choice. I am in doubts if strings or characters should be used in the spec: '(("s" . "file.pdf")) vs. '((?s . "file.pdf")), but really it does not matter. I have created some tests for this function, see the attachment. Actually I do not like such style of tests since first failure stops whole test and it is hard to get general impression to which degree the function under the test is broken, but I am not aware of a better way. Recently I asked Ihor a similar question: https://orgmode.org/list/s324b0$74g$1@ciao.gmane.io I know that functions called from one point are not in favor in org sources, but I do not mind to have additional helper function to add tests that all substitutions are properly escaped. > + (let ((ngroups (- (/ (length link-match-data) 2) 1))) > + (and (> ngroups 0) > + (progn > + (set-match-data link-match-data) > + (mapcar (lambda (n) > + (cons (number-to-string n) > + (match-string-no-properties n dlink))) > + (number-sequence 1 ngroups)))))))) Matter of taste: it seems that with (number-sequence 1 ngroups 1)) it is possible to avoid (> ngroups 0). I have spent some time evaluating how to make errors more helpful to users. I am unsure if multiline message is acceptable to dump content of specification. For a while, a place in the format where error has happened (combined with a different approach to parse format string) (defun org--open-file-format-spec (format specification) (apply #'concat (nreverse (let ((result nil) (token-end 0)) (while (string-match "%\\(.?\\)" format token-end) (let ((token-start (match-beginning 0)) (subst (match-string-no-properties 1 format))) (push (substring format token-end token-start) result) (push (if (equal subst "%") "%" (or (cdr (assoc subst specification)) (error "Unknown substitution: '%s%s'" (substring format 0 token-start) (substring format token-start nil)))) result)) (setq token-end (match-end 0))) (push (substring format token-end nil) result))))) To my surprise neither ^ nor \\` in string-match regexp works if start-pos is not zero.