1.js

const definitionsInOl = new WeakMap();

function isDefinition(varNode) {
  // Likely to be args
  if (!varNode.closest('ol')) return true;

  const previousNode = varNode.previousSibling;
  if (!previousNode) return false;
  if (previousNode.nodeType !== 3) return false;

  if (previousNode.nodeValue.trim().toLowerCase().endsWith('let')) return true;
  const previousEl = varNode.previousElementSibling;
  if (!previousEl) return false;
  return previousEl.textContent.trim().toLowerCase() === 'for each';
}

function getDefsForList(list) {
  let defs = definitionsInOl.get(list);

  if (!defs) {
    defs = [];
    definitionsInOl.set(list, defs);
  }

  return defs;
}

function main() {
  const vars = Array.from(document.querySelectorAll('var'));
  const definitions = vars.filter(v => isDefinition(v));

  loopDefs: for (const definition of definitions) {
    const name = definition.textContent.trim();
    let list = definition.closest('ol');
    if (!list) {
      const p = definition.closest('p');
      let nextEl = p && p.nextElementSibling;
      while (nextEl) {
        if (!nextEl.classList.contains('note')) break;
        nextEl = nextEl.nextElementSibling;
      }
      if (nextEl && nextEl.tagName === 'OL') {
        list = nextEl;
      }
      else {
        continue;
      }
    }

    const defs = getDefsForList(list);

    if (defs.includes(name)) {
      definition.after('(redefinition)');
      definition.style.background = '#f00';
      console.log(definition);
      continue;
    }

    defs.push(name);
  }

  const nondefs = vars.filter(v => !isDefinition(v));

  loopVars: for (const v of nondefs) {
    const name = v.textContent.trim();

    let list = v.closest('ol');

    while (list) {
      if (getDefsForList(list).includes(name)) continue loopVars;
      list = list.parentElement.closest('ol');
    }

    v.after('(definition not found)');
    v.style.background = '#f00';
    console.log(v);
  }
}

main();