-apple-system font licence possibly incompatible with licence

[oelna]

I don't mean to nag, but I recently read up on Apple's San Francisco font for a project, and its licence seems it's rather restrictive:

2. Permitted License Uses and Restrictions.
A. Limited License. Subject to the terms of this License, you may use the Apple Font solely
for creating mock-ups of user interfaces to be used in software products running on 
Apple’s iOS, OS X or tvOS operating systems, as applicable.

As this is a project that aims to allow users to create PDFs of letters for their personal or commercial use, I believe -apple-system is possibly not the best choice of default font, since it defaults to using San Francisco on a variety of modern Apple OSes. While this app itself does not seem to be in violation of the licence (which would mean quite a lot of websites were), the PDFs it generates may be.

I'd encourage users under scrutiny with licencing to change their template to use a font with a more permissive licence.

Sources:
https://developer.apple.com/fonts/ (licence RTF in the font archives)
https://en.wikipedia.org/wiki/San_Francisco_(2014_typeface)#Licensing

[omBratteng]

The font is installed on the the OS, it's just like using Arial, it's installed on the OS.
Segoe UI is the font used on Windows, Roboto is the font used on Android, then Helvetica and Arial is just a filler if it's neither of the above

[oelna]

I'd argue it's different than with Arial, as the font is not available through the OS font selection widgets and the licence specifies a narrow field of permitted use. Helvetica or Arial are clearly meant for the user to generate printable texts with them.
As I said, the problem is not the use on websites, but the files the user generates and possibly sends out to people.

[omBratteng]

Hmm, yeah I see. I just checked what fonts are embedded in the PDF, and it's there

Also read the license, here's an extract.
So I agree with you @oelna

You may not embed the Apple Font in any software programs or other products.
Except as expressly provided for herein, you may not use the Apple Font to, create,
develop, display or otherwise distribute any documentation, artwork, website content
or any other work product. 

But does it mean the font that you actually install? Or the font that is on your OS?
I'm no lawyer, it's an interesting question