This is a short tutorial with code that makes having your twine use the pronouns and honorifics that your user prefers really easy. I am sure there are better ways and more ways but I hope it is helpful.
Your tutorial is not for Twine, which is an IDE/compiler, but rather for the Twine 2 compatible story format, Harlowe.
The distinction is important as there are multiple versions of Twine and multiple story formats for each version—e.g. Twine 2 comes bundled with Harlowe, Snowman, and SugarCube. Most story formats use a somewhat different syntax relative to their contemporaries, so that makes the distinction of paramount importance. The code in your tutorial only works in Harlowe.
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The distinction is important as there are multiple versions of Twine and multiple story formats for each version—e.g. Twine 2 comes bundled with Harlowe, Snowman, and SugarCube. Most story formats use a somewhat different syntax relative to their contemporaries, so that makes the distinction of paramount importance. The code in your tutorial only works in Harlowe.