"Typography is the art and technique of arranging type to make written language legible, readable, and appealing when displayed. The arrangement of type involves selecting typefaces, point sizes, line lengths, line-spacing (leading), and letter-spacing (tracking), and adjusting the space between pairs of letters (kerning)."

https://en.wikipedia.org/wiki/Typography

You're right about the pixels. I used them because the examples set in pixels are the easiest to understand. I added a note that outside of these examples, the units used should be EM or REM. Thanks for the feedback!

Doing hateful css typography work today. It's hard enough to make ordinary stuff march in formation - I'm hitting both ceiling and deadline, which somewhat spilled over into the harshness of my comment.

That's ok. I actually wanted to include such note about the units in the first place but forgot (in the book I use REMs and pixels only as fallback but changed to pixels in the article for simplicity). Your comment reminded me to add this note in. And I know how frustrating it can be when working on typographic details on the web. Are you having any specific problems?

Nothing too specific, no, but thanks. Your tone and approach much appreciated.