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They actually specifically refer to it as "alt" in this help file:

https://support.google.com/webmasters/answer/47334

Thank you, Ria! I do notice in the Search Console help files it does mention something about tagging internal links with alt text (along with good anchor text) as a way to better optimize these links. I wonder based on that suggestion that only links that have alt text would even be considered for sitelinks? It's especially peculiar as alt isn't even a recognized attribute by the W3C standards...

Nevertheless, thank you for your response - I've found in my additional research that simply adhering the SEO best practices (along with longer standing high rankings) are the best formula for getting these sitelinks.

How does one markup their site to get the small sitelinks to appear in SERP listings as seen in the example image below?

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