Descriptions and values are drawn as a single line that never wraps.
Because a diagram is scaled to fit the width it is rendered into, the
longest label is what decides that scale: one long description makes the
whole diagram -- bit cells, indices and every other label with it --
shrink until that line fits. A register whose fields carry a sentence
each is then unreadable at any page width, and since each diagram is
measured on its own, a document full of them renders every one at a
different size.

Setting description-width wraps labels at that width instead, so the
length of a description no longer decides how large the diagram is
drawn. Values wrap at the same right edge as the description they belong
to, and the option composes with left-labels, force-descs-on-side and
ltr-bits.

Wrapping means a label is no longer one line tall, so labels can no
longer be spaced by a fixed line height. Each is now offset by the
height it actually occupies, measured before it is placed, which is why
render gained a context block.

The option defaults to none, which keeps the single-line behaviour on
the original code paths. With it unset every diagram in the gallery
renders byte-identical to before.

@@ -26,6 +26,7 @@
 /// - full-page (bool): If true, the page will be resized to fit the diagram and take the background color
 /// - all-bit-i (bool): If true, all bit indices will be rendered, otherwise, only the ends of each range will be displayed
 /// - ltr-bits (bool): If true, bits are placed with the LSB on the left instead of the right
+/// - description-width (float | none): If set, descriptions and values wrap at this width instead of being drawn on a single line

@@ -203,6 +203,36 @@ For values depending on other ranges, see #link(<format-dependencies>)[Dependenc
 }
 ```
 
+=== Wrapping descriptions <format-description-width>

@@ -206,0 +228,4 @@
+occupies, so wrapping onto several lines does not make labels overlap.
+
+```typ
+schema.render(sch, config: config.config(description-width: 300))

@@ -158,0 +193,4 @@
+    // to its left edge: exactly the box width when wrapping, an estimate from
+    // the character count otherwise
+    txt-x -= if config.description-width == none {
+      range_.description.len() * config.default-font-size / 2pt