So, I’m a bit confused about the rules of the grid system. If I want a 30px bottom margin the page, does that mean that descenders can bleed on to it as long as the baseline of the rest of the text is placed just before the 30px margin? Or is it more like, absolutely nothing can touch the margin? The Y in the picture is bleeding onto the margin. Is that OK?
There are few hard-and-fast rules.
In the case you mention, you’re trying to visually align the bottom of the line of type. So visually, the bottom of that line is the baseline, not the few descenders that extend below it.
What is px?
Visually, as Just-B said, align to the baseline. However, if you were doing this for print / advertising and you were given a text area on an ad spec, then nothing should extend that area. You’d still align to the baseline, but bring everything up a bit to fit within the text area.
What Eriskay didn’t say:
If you’re designing pages for print, you shouldn’t be using pixels as the primary unit of measure. The pixel is a relative unit; use a constant unit.
More and more I’m questioning what this education system is turning out.