Inline Highlight

<!--
  Inline Highlight - animated marker underline/fill.

  Wrap target text with class="hf-inline-highlight". Animate
  --hf-highlight-scale from 0 to 1 on the element.

  Variables. The script reads each one, falls back to the declared default on anything
  missing or unrecognised, and writes the result onto the document root, so highlights
  authored anywhere in the composition pick it up no matter when they are parsed. The
  timeline recipe below is untouched by them.

    - tint (yellow | green | blue | violet, default yellow): marker colour. yellow is the
      highlighter default, the other three ride --brand, --accent and --accent-2.
    - thickness (thin | standard | thick, default standard): height of the band behind the
      text, 0.22em, 0.38em or 0.62em.
    - origin (left | right | center, default left): edge the marker grows out of while
      --hf-highlight-scale runs from 0 to 1.

  Setting --hf-highlight-color, --hf-highlight-height or --hf-highlight-origin on an
  individual highlight still wins over the variable, so one-off overrides keep working.
-->

<style
  data-composition-variables='[
    { "id": "tint", "type": "enum", "role": "style", "label": "Tint", "description": "Marker colour. Green, blue and violet ride --brand, --accent and --accent-2.", "default": "yellow", "options": [{ "value": "yellow", "label": "Yellow" }, { "value": "green", "label": "Green" }, { "value": "blue", "label": "Blue" }, { "value": "violet", "label": "Violet" }] },
    { "id": "thickness", "type": "enum", "role": "style", "label": "Thickness", "description": "Height of the marker band behind the text, as a share of the font size.", "default": "standard", "options": [{ "value": "thin", "label": "Thin" }, { "value": "standard", "label": "Standard" }, { "value": "thick", "label": "Thick" }] },
    { "id": "origin", "type": "enum", "role": "motion", "label": "Origin", "description": "Edge the marker grows out of as the scale variable runs from 0 to 1.", "default": "left", "options": [{ "value": "left", "label": "Left" }, { "value": "right", "label": "Right" }, { "value": "center", "label": "Center" }] }
  ]'
>
  .hf-inline-highlight {
    --hf-highlight-scale: 0;
    position: relative;
    display: inline;
    z-index: 0;
  }
  .hf-inline-highlight::after {
    content: "";
    position: absolute;
    left: -0.08em;
    right: -0.08em;
    bottom: 0.05em;
    height: var(--hf-highlight-height, 0.38em);
    background: var(--hf-highlight-color, #fff06a);
    transform: scaleX(var(--hf-highlight-scale));
    transform-origin: var(--hf-highlight-origin, left center);
    z-index: -1;
  }
</style>

<script>
  (function () {
    "use strict";

    var vars =
      window.__hyperframes && window.__hyperframes.getVariables
        ? window.__hyperframes.getVariables()
        : {};

    // Unrecognised overrides return to their declared defaults.
    function pick(table, value, fallback) {
      return Object.prototype.hasOwnProperty.call(table, value) ? value : fallback;
    }

    var tints = {
      yellow: "#fff06a",
      green: "var(--brand, #34d399)",
      blue: "var(--accent, #38bdf8)",
      violet: "var(--accent-2, #a78bfa)",
    };
    var heights = { thin: "0.22em", standard: "0.38em", thick: "0.62em" };
    var origins = { left: "left center", right: "right center", center: "center" };

    var root = document.documentElement;
    root.style.setProperty("--hf-highlight-color", tints[pick(tints, vars.tint, "yellow")]);
    root.style.setProperty(
      "--hf-highlight-height",
      heights[pick(heights, vars.thickness, "standard")],
    );
    root.style.setProperty("--hf-highlight-origin", origins[pick(origins, vars.origin, "left")]);
  })();
</script>

<!--
  Timeline integration:

  tl.to(".hf-inline-highlight", {
    "--hf-highlight-scale": 1,
    duration: 0.55,
    ease: "power2.out",
    stagger: 0.12,
  }, startTime);
-->