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Date:         Tue, 3 Jun 2014 08:47:57 +0930
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From: Will Robertson <wspr81@GMAIL.COM>
Subject: Re: 'Preseting' keys
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Status: R

Hi Joseph,

I think the name and the functionality are sensible.

On 3 Jun 2014, at 12:47 am, Joseph Wright <joseph.wright@MORNINGSTAR2.CO.=
UK> wrote:

> However, there are cases where you'd like to 'preset' the key every
> time. Currently, that would require
>=20
>    \cs_new_protected:Npn \foo #1#2 % #1 =3D keys
>      {
>        \keys_set:nn { mymod }
>          {
>            key-a =3D new-value ,
>            #1
>          }
>=20
> but that is not that efficient and also not that clear.
>=20
> An alternative approach is to provide a method to 'preset' keys from
> within the key system, something like
>=20
>  \keys_define:nn { mymod }
>    {
>      key-a .tl_set:N =3D \l_mya_tl ,
>      key-a .preset:n =3D value
>     ...
>    }
>=20
> where the presetting can avoid having to parse the keys each time it's
> run (cf. what happens in template).


The first case is what I do in fontspec (but there=92s lots I do in fonts=
pec that I probably shouldn't).
I suspect that I=92d need to play around with some interfaces to figure o=
ut how this would change things.
Thinking along these lines:


>    \cs_new_protected:Npn \foo #1#2 % #1 =3D keys
>      {
>        \keys_define:nn { mymod }
>          {
>            key-a .preset:n =3D new-value ,
>          }
>       \keys_set:nn { mymod }
>          {
>            #1
>          }


One thing that becomes a bit harder is unsetting the preset; if I then ne=
ed to run \keys_set:nn again the preset would either need to be grouped o=
r explicitly disabled.

(E.g., when setting Letters=3DSmallCaps for the small caps font before mo=
ving on to another font shape.)

So at least in my use case, and only thinking very briefly about it, I=92=
m not sure if this interface would be a advantage for fontspec =97 but th=
at=92s not to say that it=92s not a bad idea, nor either that fontspec co=
uldn't be re-jigged to be a bit more sensible in such matters.

Cheers,
Will