The core plug-in provides a recursive descent WikiText parser which loads it's individual rules from individual modules.
Thus a developer can provide additional rules by using ``module-type: wikirule``. Each rule can produce a list of parse-tree nodes.
A simple example for a wikirule producing a ``<hr>`` from ``---`` can be found in [[horizrule.js|$:/core/modules/parsers/wikiparser/rules/horizrule.js]]
HTML tags can be embedded into WikiText because of the [[html rule|$:/core/modules/parsers/wikiparser/rules/html.js]].
This rule matches HTML tag syntax and creates ``type: "element"`` nodes.
But the html-rule has another special purpose. By parsing the HTML tag syntax it implicitly parses WikiText widgets.
It the recognises them by the $ character at the beginning of the tag name and instead of producing "element" nodes
The [[Widgets]] part will reveal why this makes sense and how each node is transformed into a widget.
Another special characteristic of the html-rule or the parse nodes in general is the attributes property.
Attributes in the parse-tree are not stored as simple strings but they are nodes of its own to make indirect text references available as attributes as described in [[Widgets]]:
