What does "as to" stand here for or what does it mean? Does it have a similar meaning to "regarding", "as for", "as regards"?<br/><br/>"If you are in any doubt <b>as to</b> whether you should be doing these exercises, consult your doctor."<br/><br/>or<br/><br/>"I have my doubts<b> as to</b> the wisdom of going ahead with such a project."<br/><br/>Thank you very much.