Line Chart

• series[].data is aligned index for index with categories; when the lengths differ the shorter side wins.
• null, NaN and Infinity are gaps: the mark is skipped and a line breaks there instead of connecting across. A gap is never drawn as 0.
• The value domain is [min(0, min), max(0, max)] over all series, so the value axis always includes 0 and is never log-scaled or clamped.
• The identity of a series is id ?? name. Two series or slices sharing an identity get distinct keys (a, a#1, ...), and in development mode the chart logs one warning for a duplicate explicit id and for a data array whose length differs from categories.
• A flat domain (every value equal) is expanded so the axis never collapses, and ticks are rounded to the precision their step needs.
• series[].color or slices[].color is optional; without it the marks use a round-robin over the eight --kui-chart-series-1..8 tokens in the order given.

• Hiding a series does not recompute the value-axis domain, so the remaining series keep a stable scale across toggles.
• Hovering a legend item highlights the matching mark, and hovering a mark highlights its legend entry. Hidden items stay interactive; "every series hidden" is a legend-only state and not the empty composition.
• A hidden item is marked by more than its pressed state: the label is struck through and the swatch becomes an outline.

Standalone legend

Every chart implements KuiChartLegendSource: a public legendItems() and hoveredLegendId() read surface plus toggleLegendItem(id) and setHoveredLegendId(id). Pass the chart through a template reference variable to kui-chart-legend to render the legend anywhere, and set [legend]="false" on the chart so it is not drawn twice. Project a kuiChartLegendItem template (context KuiChartLegendItemContext: $implicit is the KuiChartLegendEntry, hovered the cross-highlight state) to replace the default button markup; wiring the toggle and hover calls is the template's job.

<kui-line-chart
  #chartRef
  ariaLabel="Sessions per day"
  [series]="series"
  [categories]="categories"
  [legend]="false"
/>
<kui-chart-legend [chart]="chartRef" />

• size is sm, md or lg (default md): a plot height of 200, 280 or 360px.
• The chart measures its container with a ResizeObserver and draws at one user unit per CSS pixel, so text, strokes and marks keep their pixel size at any width. The axis padding fits the widest measured tick label and the axis title.
• Server rendering and the first client render use a nominal width (320, 480 or 640px) inside a graphic whose height is already final, so hydration does not shift the layout.
• Tick labels are thinned by their measured width plus an 8px gap so they never overlap, and a label wider than its slot is cut with an ellipsis (the full text stays in the element <title>). Axis text defaults to --kui-text-sm-size; the --kui-chart-axis-text-font-size token changes it.
• Axis titles come from axes.xTitle and axes.yTitle and are drawn in the SVG. There is no built-in zoom, pan or decimation: aggregate very dense data before passing it in.

• The line skeleton is a wavy sparkline silhouette of shimmering dots built from [kuiSkeleton].
• An empty or missing input (no non-gap value anywhere) always renders the empty composition: a dashed border, a faded chart icon and the "No data" text. It is not the kui-empty-state component.
• The loading and empty texts are chart messages.

protected formatTooltip(point: KuiChartPoint): string {
  return `${point.categoryLabel}: $${point.value.toLocaleString('en-US')}`;
}

• tooltip overrides the default text: <series> · <category>: <value>.
• valueFormat defaults to the compact notation of the locale (1.2K and 3.4M in English, 1,5 Mio. in German). It formats axis ticks and the default tooltip and legend numbers, and is never used for the alt-table, which shows exact values.
• The tooltip is dismissible (Escape closes it without moving focus or the pointer until a new trigger) and persistent (it stays until hover or focus ends). It follows the pointer and ignores pointer events, so it is not hoverable (WCAG 1.4.13); see Known gaps.
• Accessible names, role descriptions, the loading and empty texts, the table headers and the point text are chart messages. Every chart takes a messages input for one-off overrides.

• The alt-table is the accessible-charts recommendation of pairing a graphic with a tabular alternative, not a decorative duplicate. It lists the visible series with exact (not compact-formatted) numbers and has a caption with the chart name.
• It lists every point of a dense chart whatever the chart draws.
• The Table button keeps keyboard focus when the view switches.

• With more than one series, marks use a marker shape per series index (circle, square, diamond, up and down triangle, cross, plus, star) and the legend swatch shows the same shape. A single series stays circles, and hiding another series never changes the shape.
• patterns (default false) fills each series with one of eight hatch patterns, a tinted ground with a hatch in the full series colour, and the legend swatch becomes a patterned square. On a line chart it applies to area. Pattern ids are unique per chart instance, so many charts on one page never collide.
• In forced colours (Windows High Contrast) the chart draws with the system colours CanvasText, Canvas, GrayText and Highlight only. Series then differ by hatch pattern, by dash (lines) and by marker shape; patterns and dashes turn on automatically.

• ArrowLeft and ArrowRight move along the category axis in the same series, ArrowUp and ArrowDown between series at the same category, and Home and End jump to the first and last category of the series.
• Escape dismisses the tooltip; Enter and Space on a legend item toggle it.
• The roving position is a key (series and category), not an index, so hiding a series moves it to the nearest remaining mark and re-focuses that mark if focus was inside the chart. Focus mirrors hover: the focused mark highlights its series and opens the tooltip.

• A line chart draws one DOM mark per point up to 500 marks (KUI_CHART_MARK_LIMIT). Above that it draws only the mark that holds the tab stop; the keyboard model is index based and the table still lists every point.
• Library measurements in Chromium (a two-series line chart and a one-series scatter chart of the same point count): 500 points paint in 46 ms with 1,629 DOM nodes, 2,000 points in 115 ms with 6,123 nodes and 5,000 points in 259 ms with 15,123 nodes. Hiding a series on the 2,000-point line chart paints in 27 ms. Decimation is out of scope.