Languagesystem question

The auto-generated languagesystem for my Arabic font is like this:

As you notice I have a localized lookup for Arabic language as well which is reflected in this auto-generation.
So far this shouldn’t be a problem because that localized substitution doesn’t have a different substitution scheme in the default language setting, which is also auto-generated as Arabic. But I was thinking that as I go, I might encounter the cases that do have a different substitution in default setting and it might cause a conflict. So I want to set the languagesystem in a way that the script is defined as Arabic and the default language as Persian. And I set it like this:

Does it look right to you? I clicked on update features button and it didn’t complain!

If at all it would be languagesystem arab FAR; but you do not have to write it yourself, it is autogenerated as soon as you have a respective language statement somewhere in your feature code.

Okay thanks. I’ll leave it on automatic.
The thing is that there won’t be any specific feature for Persian. I see everything in Persian view, whether I know it or not! if anything, there will be some specifics for other languages including Arabic which may then be in conflict with the default setting which is also defined as Arabic.

Then you do not need to add Persian to the languagesystems.

Which default setting?

Well the auto generated languagesystem the second line reads ‘languagesystem arab dflt’ (lower case). This is about the language not the script isn’t it?
I looked at OT specifications and it says the upper case DFLT is related to the script and the lower case dflt is related to the language. Then the tag ‘arab’ is for the script and the tag ‘ARA’ is for the language. I’m pretty confused here I must say!
I’ll leave it on ‘auto’ and see what happens.

arab dflt just means the Arabic script without any language specification.

The whole languagesystem thing has nothing to do with language support of the font. It only refers to the scripts and languages some language-specific OpenType features are registered in. The fact that not all languages are listed does not mean you cannot type these languages with your font.

Thanks so much. I think that’s all I needed to know from the beginning!