I think the author missed there something and was thinking of the seriffed capital ›I‹, which is quite distinct in Verdana, when he wrote this.

Ha, the exact same thing struck me when I read that bit today! I also wondered about the cap I, but it's only one character! It's quite a silly thing to say Verdana is a semi-serif, I think.

Also the j and 1, maybe. Agree it seems a wrong/silly classification.

Si

And in any case, those serifs don't disappear at small sizes. What could Davidow be talking about?

Perhaps he is referring to the way that turning off font-smoothing at a small size threshold and rendering tiny text as a high-contrast pixel-font bitmap will render C, for instance, as three straight lines, with no "semi-serifs" at the terminals.

This is not font-specific; however the distinction for Verdana is that the small-size bitmap was designed that way, with separate size-specific forms, rather than having the pixel-font as a compromise or adjustment made to the "proper" higher-res iteration.