jquery DOMEval函数的理解

function DOMEval( code, doc, node ) {
        doc = doc || document;

        var i,
            script = doc.createElement( "script" );

        script.text = code;
        if ( node ) {
            for ( i in preservedScriptAttributes ) {
                if ( node[ i ] ) {
                    script[ i ] = node[ i ];
                }
            }
        }
        doc.head.appendChild( script ).parentNode.removeChild( script );//特别是这一句代码怎么理解
    }