Form Group

Use the formGroup patch to lay out label + input pairs inside a <fieldset>. Unlike other patches that only style the element itself, formGroup defines a grid layout contract for its children: legend, label, inputs, and help text (p).

Customization

Must see the source of patch at the bottom of each patch page to understand the structure then code it still code as html native element.

There are four levels of customization, in increasing order of effort:

Patch props. Each patch exposes a small, stable set of props—typically fewer than five. Lowest friction.
Context attributes. Use dataTone, dataSize, and dataDensity on a container to shift tone, size, or density for an entire subtree without touching individual elements.
Inline override. Native-wins merge strategy: any property set directly on the element overrides the patch value.
Create a variant. Clone a similar patch and edit it. Use this only when you need a reusable custom version.

Formulas

Unit - U = fontSize / 4 - convert final values with themeSpacing(n).

Size - n = intrinsic text lines, w = wrapping level, d = density factor:

height        = (n * 6 + 2 * d * w) * U
paddingBlock  = d * w * U
paddingInline = ceil(3 / w) * d * w * U
radius        = d * w * U

Base density d = 1.5:

U	w=0	w=1	w=2	w=3
height (`n = 1`)	6	9	12	15
paddingBlock	0	1.5	3	4.5
paddingInline	3	4.5	6	4.5
radius	0	1.5	3	4.5

Tone - K = N / 2 where N is the palette length. For N = 18, K = 9.

Role	Shift	n=0
Background	parent +/- n	0
Text	bg + K	6
Border	bg + K/2	3
Hover	bg + 2K/3	4
Selected / Focus	above +/- K/3	2-4

State shift range: K/3 <= delta <= 2K/3.

formGroup

import { type PartialElement, toState, type ValueOrState } from "@domphy/core";
import {
  type ThemeColor,
  themeColor,
  themeDensity,
  themeSize,
  themeSpacing,
} from "@domphy/theme";

/**
 * Layout patch for a group of form fields. Arranges a `<legend>`, `<label>`s,
 * controls, and helper `<p>`s in a grid — labels beside controls (horizontal)
 * or stacked above them (vertical). Apply to a `<fieldset>` element.
 *
 * @hostTag fieldset
 * @param props.color - Theme color tone (`ValueOrState<ThemeColor>`) for legend/text/surface. Defaults to "neutral".
 * @param props.layout - Field arrangement, "horizontal" (label beside control) | "vertical" (label above). Defaults to "horizontal".
 * @example { fieldset: [{ legend: "Profile" }, { label: "Name" }, { input: "" }], $: [formGroup({ layout: "vertical" })] }
 */
function formGroup(
  props: {
    color?: ValueOrState<ThemeColor>;
    layout?: "horizontal" | "vertical";
  } = {},
): PartialElement {
  const { layout = "horizontal" } = props;
  const color = toState(props.color ?? "neutral", "color");

  const isVertical = layout === "vertical";

  return {
    _onInsert: (node) => {
      if (node.tagName !== "fieldset") {
        console.warn(`"formGroup" patch must use fieldset tag`);
      }
    },
    style: {
      margin: 0,
      paddingInline: (listener) => themeSpacing(themeDensity(listener) * 3),
      paddingBlock: (listener) => themeSpacing(themeDensity(listener) * 3),
      border: "none",
      borderRadius: (listener) => themeSpacing(themeDensity(listener) * 2),
      fontSize: (listener) => themeSize(listener, "inherit"),
      backgroundColor: (listener) =>
        themeColor(listener, "inherit", color.get(listener)),
      display: "grid",
      gridTemplateColumns: isVertical
        ? `minmax(0, 1fr)`
        : `max-content minmax(0, 1fr)`,
      columnGap: themeSpacing(4),
      rowGap: themeSpacing(3),
      alignItems: "start",
      "& > legend": {
        gridColumn: "1 / -1",
        margin: 0,
        fontSize: (listener) => themeSize(listener, "inherit"),
        fontWeight: 600,
        paddingBlock: (listener) => themeSpacing(themeDensity(listener) * 1),
        borderRadius: (listener) => themeSpacing(themeDensity(listener) * 2),
        color: (listener) =>
          themeColor(listener, "shift-9", color.get(listener)),
        backgroundColor: (listener) =>
          themeColor(listener, "inherit", color.get(listener)),
      },
      "& > label": {
        gridColumn: "1",
        alignSelf: "start",
        margin: 0,
        paddingBlock: (listener) =>
          isVertical ? "0px" : themeSpacing(themeDensity(listener) * 1),
      },
      "& > label:has(+ :not(legend, label, p) + p)": {
        gridRow: isVertical ? "auto" : "span 2",
      },
      "& > :not(legend, label, p)": {
        gridColumn: isVertical ? "1" : "2",
        minWidth: 0,
        width: "100%",
        boxSizing: "border-box",
      },
      "& > p": {
        gridColumn: isVertical ? "1" : "2",
        minWidth: 0,
        margin: 0,
        marginBlockStart: `calc(${themeSpacing(2)} * -1)`,
        fontSize: (listener) => themeSize(listener, "decrease-1"),
        color: (listener) =>
          themeColor(listener, "shift-9", color.get(listener)),
      },
    },
  };
}

export { formGroup };

</div>