docs: function _getVirtualRect (context, mergedStyle) {
    const ct = context._getParentRect()
    const rect = ['width', 'height'].reduce((pre, key) => {
      const msv = mergedStyle && mergedStyle[key]
      pre[key] = msv ? parseFloat(msv) : ct[key]
      return pre
    }, {})
    return rect
  }