async function query( target, pelh = bs.page ) {
    if ( target.parentType === "iframe" ) {
      pelh = await pelh.contentFrame();
    }
    if ( !pelh ) {
      throw new Error( `Cannot find parent of ${ target.target } `
        + `(${ target.css ? "CSS": "XPath" }: ${ target.selector })` );
    }
    const elh = target.css ? await pelh.$( target.selector ) : await queryXpath( target.selector, pelh );
    if ( !elh ) {
      throw new Error( `Cannot find target ${ target.target } `
        + `(${ target.css ? "CSS": "XPath" }: ${ target.selector })` );
    }
    return elh;
  }
@param {Target} target
@param {ElementHandle} pelh
@returns {?ElementHandle}