org-mode export to html fails for unknown link types - telephone links

[Eugen Stan]

Hi,

I am building my wedding page with org mode. Yay!.
I tried to add telephone links so people can click on the link and it 
will do something useful.

I used this markup [[tel:(+40)55-555-555][(+40)55-555-555]] to produce 
something like <a href="tel:(+40)55-555-555">(+40)55-555-555</a> .

However It failed because the tel: is not recognized link.
I believe the default behavior of failing to export when encountering an 
unknown link type is not ok.

IMO org-mode export should allow export for unknown links.
Support for tel: links might be added to org-mode by default since it is 
simple to add and quite useful, at least in HTML export .
See https://css-tricks.com/the-current-state-of-telephone-links/ .

It seems it might work in PDF exports as well 
https://community.adobe.com/t5/acrobat-reader-discussions/how-to-make-clickable-phone-numbers-in-pdfs/m-p/5822600 
.

Regardless, having the export fail is a bug IMO.


To build my website I followed a slightly updated version of 
https://systemcrafters.net/publishing-websites-with-org-mode/building-the-site/ 
.

I made it work with some customization but I do believe the default

(require 'ox-publish)
(require 'ol)

(org-link-set-parameters "tel"
                         :export #'org-tel-export)

(defun org-tel-export (link description format _)
  "Export a tel link from Org files."
  (let ((path link)
        (desc (or description link)))
    (pcase format
      (`html (format "<a class=\"org-tel-href\" href=\"tel:%s\">%s</a>" 
path desc))
      (`latex (format "\\href{%s}{%s}" path desc))
      (`texinfo (format "@uref{%s,%s}" path desc))
      (`ascii (format "%s (%s)" desc path))
      (t path))))

(setq org-publish-project-alist
      `(("nunta-org-site"
         :recursive t
 ...... )

(org-publish-all t)