function validate_required(field,alerttxt) {
  with (field) {
    if (value==null||value=="") {
      alert(alerttxt);return false
    }
    else { return true }
  }
}

function validate_email(field,alerttxt) {
  with (field) {
    apos=value.indexOf("@")
    dotpos=value.lastIndexOf(".")
    if (apos<1||dotpos-apos<2) {
      alert(alerttxt);return false
    }
    else { return true }
  }
}

function validate_form(thisform) {
  with (thisform) {
    if (validate_required(name,"Please enter your name")==false) {
      name.focus();return false
    }
    if (validate_required(phone,"Please enter your telephone number")==false) {
      phone.focus();return false
    }
    if (validate_required(email,"Please enter your email address")==false) {
      email.focus();return false
    }
    if (validate_email(email,"Please enter a valid email address")==false) {
      email.focus();return false
    }
  }
}