function quoteXPathAttributeString(string) {
    "use strict";
    if (/"/g.test(string)) {
        return 'concat("' + string.toString().replace(/"/g, '", \'"\', "') + '")';
    } else {
        return '"' + string + '"';
    }
}
Prepares a string for xpath expression with the condition [text()=].

@param  String  string
@return String