the %custom slot should just be a way to make custom slot types with json or a special editor
Not very helpful on what it would be
like something that allows people to make any slot they want by treating the special slot types like the stage or a sprite
Will you come up with an example/mockup?
slot only block picker to the left
blocks to the right
that block thing at the upper right corner is the slot preview
render:: control hat //uses a modified pen to render the morph
close path::pen //closes the path
begin path::pen //beings the path
stroke::pen //draws the lines
when edited by block ((value))::control hat //this signals when it gets edited by the block
when created::control hat
evaluate::control hat //basically the evaluate() method
report[]
signal edited []::control // signals that the slot has been edited
set width to ()::looks
set height to ()::looks
set extents to [list]::looks
(width::looks)
(height::looks)
(extents::looks)
create dialog titled [title] \n when mouse action done ({\n $-0::cap sensing } ((action)) @< @>) \n rendered ({}@>) \n with buttons [name] $arrowRight ({}@>) @< @:> ::sensing //creates a custom dialog with custom rendering
create resizable dialog titled [title] \n when mouse action done ({\n $-0::cap sensing } ((action)) @< @>) \n rendered ({}@>) \n with buttons [name] $arrowRight ({}@>) @< @:> ::sensing //creates a custom dialog with custom rendering but resizable
//common block variations when I am [mouse moved V]
the %custom is a good idea! Custom slots are Awesome! 
So you basically want Morphic.js’s API as blocks?
Interesting idea, but no; would probably be either too confusing or something only a few people need.
Now that you have examples, next, come up with use cases.
What slots could one want to create with this?
this may be too confusing to work, but incredibly useful.
for my XML script builder project, I had to resort to using object inputs for XML blocks since there wasn’t any custom stuff.
The “Writing and Formatting” library or whatever it’s called uses readonly numeric slots, which is strange but it must be like that currently because we have no custom inputs.
I feel like a better idea would be to use any symbol for an object input:
Although this could get confusing; as symbols can already be added; so maybe add a rounded border around symbol input slots?
EDIT: Here’s a mockup with a background around input slots:
imo the background should be bigger. but this is really great/smart!