[NTG-context] Re: how to define an environment with key=value arguments

[Wolfgang Schuster <wolfgang.schuster.lists@gmail.com>]

Henning Hraban Ramm schrieb am 08.09.2023 um 12:22:
> Hi,
> for an involved image placement (full page image starting each 
> chapter, several stacked elements), I’d like an environment that 
> accepts key-value arguments, like
>
> \startMyFigure[page=left,title={My caption}]
> \externalfigure[dummy]…
> \stopMyFigure
>
> I don’t think that a real float makes sense, even if the interface 
> looks similar, since it’s always a full page in a fixed place, I need 
> no numbering and can place the caption myself.
>
> Does it make sense to use \definestartstop?
> How would I “plugin“ the argument handling?
>
>
> Or should I better define start and stop separately?
>
> \def\startMyFigure[#1]{
> % e.g. use utilities.parsers.settings_to_hash(#1)
> }
> \def\stopMyFigure{}
>
>
> Probably I’ll need to catch the content (\externalfigure, might become 
> more) and use it in a \setlayer – so perhaps something like
>
> \definebuffer[MyFigure]
> \define\stopMyFigure{%
>  \setlayer[page]{\getMyFigure}}}
> }
>
> ?
> But then I don’t know how to handle the arguments.
>
> Probably it makes most sense to do it in Lua, like
>
> \startluacode
>      interfaces.implement {
>          name      = "startMyFigure",
>          public    = true,
>          arguments = {"hash",},
>          actions   = function(h, a)
>         -- …
>         end, }
> \stopluacode
>
> But I didn’t find how to do environments.

When you just need an environment with a optional argument to pass user 
values you can
use the userdata environment but be aware that you have some limitations 
(like verbatim)
because the mechanism uses a buffer to store the content.

For images (and other content) which are placed on a separate page at 
the start of a chapter
you can use the pageinjection mechanism which was added for this purpose.

Wolfgang

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