I have succeeded in the goal, but It probably can be done better.
After a study of the type constructor "tag" uses, specially in
"formtag", "select" and "option", I have a better understanding of it.
Although it is well explained in the manual (XML section), it is not
easy to understand when there are several abstract concepts, that your
mind easily skips.
Specially the type constructor "tag" it is confound with the value "tag"
(that builds up xml subtrees with specific tag) but the different
parameters they take augments the confusion.
con svgTag = fn (attrs :: {Type}) =>
ctx ::: {Unit} ->
[[Svg] ~ ctx] =>
unit -> tag attrs ([Svg] ++ ctx) ([Svg] ++ ctx) [] []
I know now that this is well constructed (specially the outer context
requirement, and the required context for the inner tags) specially when
used with container tags like "g" for grouping elements
val g : svgTag (commonAttrs ++ langSpaceAttrs)
so the required inner context match the inner tags outer context
requirement.
>
> val svg : unit -> tag svgTagAttrs body svg [] []
>
> There is a quirk, since SVG can be an html level tag but also an
> inner svg fragment container, but I have not treated this case.
The "svg" tag establishes a new coordinate system. The fragments can be
set up with the grouping tag "g", without redefining the coordinate system.
I could not find a way to encode two possible outer context requirements
for the svg tag.
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