function WebForm_PostBackOptions(eventTarget, eventArgument, validation, validationGroup, actionUrl, trackFocus, clientSubmit) {
    this.eventTarget = eventTarget;
    this.eventArgument = eventArgument;
    this.validation = validation;
    this.validationGroup = validationGroup;
    this.actionUrl = actionUrl;
    this.trackFocus = trackFocus;
    this.clientSubmit = clientSubmit;
}
 
function WebForm_DoPostBackWithOptions(options) {
    var validationResult = true;
    if (options.validation) {
        if (typeof(Page_ClientValidate) == 'function') {
            validationResult = Page_ClientValidate(options.validationGroup);
        }
    }

    if (validationResult) {
        if ((typeof(options.actionUrl) != "undefined") && (options.actionUrl != null) && (options.actionUrl.length > 0)) {
            theForm.action = options.actionUrl;
        }
        if (options.trackFocus) {
            var lastFocus = theForm.elements["__LASTFOCUS"];
            if ((typeof(lastFocus) != "undefined") && (lastFocus != null)) {
                if (typeof(document.activeElement) == "undefined") {
                    lastFocus.value = options.eventTarget;
                }
                else {
                    var active = document.activeElement;
                    if ((typeof(active) != "undefined") && (active != null)) {
                        if ((typeof(active.id) != "undefined") && (active.id != null) && (active.id.length > 0)) {
                            lastFocus.value = active.id;
                        }
                        else if (typeof(active.name) != "undefined") {
                            lastFocus.value = active.name;
                        }
                    }
                }
            }
        }
    }

    if (options.clientSubmit) {
        __doPostBack(options.eventTarget, options.eventArgument);
    }
}

OnPreRender
 1 if ((this.Page != null) && base.IsEnabled)
 2      {
 3            if ((this.CausesValidation && (this.Page.GetValidators(this.ValidationGroup).Count > 0)) || !string.IsNullOrEmpty(this.PostBackUrl))
 4            {
 5                  this.Page.RegisterWebFormsScript();
 6            }
 7            else if (!this.UseSubmitBehavior)
 8            {
 9                  this.Page.RegisterPostBackScript();
10            }
11      }
12

DoPostBackWithOptions
1private string gDoPostBackWithOptions = "WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions(\"{0}\", \"{1}\", {2}, \"{3}\", \"{4}\", {5}, {6}))";

IButtonControl button = (IButtonControl)control;

                    if ((button.CausesValidation && (this.Page.GetValidators(button.ValidationGroup).Count > 0)) || !string.IsNullOrEmpty(button.PostBackUrl))
                    {
                        strOnClickScript = string.Format(gDoPostBackWithOptions, control.ClientID, button.CommandArgument, button.CausesValidation.ToString().ToLower(), button.ValidationGroup, button.PostBackUrl, "false", "true");
                    }
                    else
                    {
                        strOnClickScript = Page.ClientScript.GetPostBackEventReference(control, button.CommandArgument);
                    }