One of the goals of the Tw2parser plugin is to hide the Classic macros from tiddlers of types other than text/x-tiddlywiki. This is achieved by having the parser prepend the macro definitions to the 'local' parse tree (see around line 60 wikitextparser.js), making them only visible in text/x-tiddlywiki tiddlers and typed-blocks. At present all text based Classic macros are in the same file.
As all global Tw5 macros are visible in all tiddlers (including text/x-tiddlywiki tiddlers), there is a name-space conflict between Classic and tw5 macros. For macros that are defined using tiddlytext (ie /define() /end blocks) the local defined Classic definition will override the global Tw5 macros (which is what we want).
For cases where simple overriding is not sufficient, the tw2parser plugin also has a 'macro name adapter' module (macroadapter.js) to move the Classic macros names to a new names -
An example is the {{{tabs()}}} macro which is mapped to {{{__system_tabs()}}}
so the user still types {{{tabs()}}} but this is mapped to {{{__system_tabs()}}} in the parser which is what appears in the file macrodefs.tids
There is also the facility to manipulate the parameters via {{{params=macroadapter.paramadaptername}}}
This is used in the 'tabs' macro where there is a variable number of parameters that must be mapped into fixed number of tw5 macro parameters.
The implementation of the tabs macro is rather sophisticated, the parameters are put into maps from tab-tiddername to tab-property (properties are cookies, prompts and labels) implemented as jsons.
