Creating an enclosing widget

In SugarCube, the <<if>> macro has a boolean parameter, as well as a closing tag, <</if>> or <<endif>>.

Can I, using <<widget>>, create something similar? I want to make a widget that can accept parameters, as well as having a closing tag.

Example:

<<showIf "showDesc" "Nature">>The tree is green.<<endShow>>

This will only show the "The tree is green." text if showDesc is true and settings.describe is "Nature".