A Nav component should always display its text attribute, even if the nav item has been previously selected

[lizadaly]

Because a Nav is a special case of Choice, once a Nav item is clicked it isn't possible to display it again with a different visible string.

Consider the following:

<Nav text="Go here..." tag="test" next="chapter2">

Then later in the story:

<Nav text="Go back..." tag="test" next="chapter2">

It's allowable to have multiple occurrences of Nav items, but because the choice is considered resolved, its text will not be displayed, and any future occurrence of a Nav of tag chapter2 will always display "Go here," and never "Go back." "Go back" would only appear if the early Nav instance remained unclicked.