@GWicke has repeatedly said that he is not happy when JSON is created via template parameter expansion, as used by the <graph> tag:

<graph>{
  "a": "{{{templateArgA}}}",
  "b": {{{templateArgB | { } }}}
}</graph>

I would somewhat agree that having an arbitrary text expansion seems ripe for abuse, yet at the same time offers tremendous power that has been heavily used by many templates, along side Lua JSON generation.

I'm starting this RFC to find a better middle ground that offers both the power and flexibility, while also being more palatable architecturally and easier to use for Parsoid et al.

Technically, template param expansion is similar to a User Defined Function - where Wiki contributors define a custom function that takes some arguments, and generates a valid JSON blob. Assuming that HTML tag attributes could have any length, the above example can be written as:

<graph argA='"{{{templateArgA}}}"' argB="{{{templateArgB | { } }}}" >{
  "a": (argA),
  "b": (argB)
}</graph>

where the argA and argB are first resolved by the Parser. The JSON generator then requires each argument to be a valid JSON (a properly quoted string, number, list, object, null, true, false). Each argument placeholder can only be placed in the "valid" JSON value spots:

{
  "a": (argA),      // valid
  "b": "(argB)",    // ignored
  "c": (argC).5,    // not valid - concatenating two part of a number
   ...
}

The problem with this approach is that most likely the community will immediately want conditionals, e.g. insert argA only if argA is given, otherwise don't even add the "a" element.

Optionally we might also want to support comma-separated list of JSON, allowing authors to write "c": [ (argA), (argB) ] (list concatenation), or `"d": { (argA), (argB) } (object property merging). This is TBD, possibly not worth it because it can be done with Lua.

Given this generic facility, we could disable any kinds of template parameter expansion inside the tag (after some migration time).