How to specify relative font sizes?

[davidchisnall]

Looking at the code for the verbatim environment, it sets the font size to the current size - 3 (pt?). I was not able to work out how to write that in the declarative syntax. The manual mentions that you can write things in terms of the page height or width.

[Omikhleia]

it sets the font size to the current size - 3 (pt?)

It still does? This is likely wrong, there's no reason for using a "hard-coded" 3pt smaller font, not depending on what was the original size. ^^
What you are looking for might be a font size in "em" (e.g. 0.8em = slightly smaller than the current font size)

[alerque]

Yes, this does look wrong.

[davidchisnall]

This is how I read the code in verbatim.

I was trying to achieve the same result as this environment.

[Omikhleia]

N.B. I see from some traces of yours in #1837 that you've resilient.sile installed, so be aware that when using the "resilient.book" class (instead of the default "book" class), the \verbatim:font hook (and actually the whole default verbatim package) is not used in principle.
Anyhow, this -3pt correction is a bad default, and the right way to pick a smaller or bigger font than the current font is to use a relative unit, typically in "em". If your initial font, say, is at 10pt, then 1em for it = 10pt, and an environment switching to 0.9em would thus be in 9pt (and so on, the same environment nested would be in 8.1pt)

[Omikhleia]

P.S. Just in case old-school typographers pass by, using "em" ratios is a technical answer, and not a "typographical" one in the stricter sense (in the old era of metal typography, a compositor would have frown upon the above 8.1pt of course).

[alerque]

The easiest ways is to use relative units. For example the em unit is typically the size of the current font, so \font[size=0.95em]{this is 5% smaller} would make a smaller size relative to the surrounding context.

Relative sizes are typically not specified as with an absolute value offset from a relative size. You could do that, but you'd probably need to make a small wrapper function of your own to accomplish it:

SILE.registerCommand("three-smaller", function (options, content)
   options.size = SILE.types.measurement("1em"):absolute() - SILE.types.measurement("3pt")
   SILE.call("font", options, content)
end)

Then in your content, you could use \three-smaller{this is 3 hard points smaller than the surrounding context}.