Global variables access within attributes will automatically trigger a refresh if the attribute text changes, but that wasn't happening for transclusions.
The objective is to add a $depth attribute so that it is possible to reach up to retrieve the parameters of ancestor transclusions. However, doing so requires changing the encoding of parameter names so that it is not possible for a user parameter to clash with an attribute like $depth. So now we have to double up dollars on any attribute names seen by the parameters widget, just like with the transclude widget itself.
Can invoke any functions, not just those start with a period. And can pass zero parameters (in contrast when invoked as a custom filter operator there's no way to omit the first parameter).
So far it appears to be totally backwards compatible... In practice, I think maybe this and the conversion of the other macros should go into a separate subsequent PR.
The basic idea is that if we don't find a variable `foo` then we fallback to retrieving the value from the tiddler `$:/global/foo`, if it exists.
This allows us to replace the usual importvariables-based mechanism for global definitions, avoiding cluttering up the variable namespace with every macro.
In order to permit subprocedures to be overridden, we also introduce a mechanism for conditional definitions: preceding the word definition|procedure|function|widget with a + causes the definition only to occur if the specified variable doesn't already exist. In the next commit we'll apply this mechanism to the tabs macro
These improvements rely on the new JSON operators to be useful. Those improvements were originally in #6522 but now there's an updated version in #6666. Managing things is simpler if I merge these changes now
An experiment to try out using the new JSON operators for rendering the JSON parse tree that we get back from the wikify widget.
As usual with these experiments, this one is going to require quite a lot more work to finish up:
* The formatting is via direct styles rather than classes
* The formatting for attributes and properties is not yet completed
* The same thing needs to also be done to the widget tree preview
