vue3-yuanma/packages/runtime-dom/src/modules/class.ts

// compiler should normlaize class + :class bindings on the same element
// into a single binding ['staticClass', dynamic]

export function patchClass(el: Element, value: string, isSVG: boolean) {
  // directly setting className should be faster than setAttribute in theory
  if (isSVG) {
    el.setAttribute('class', value)
  } else {
    el.className = value
  }
}