# Determine the Base User Exit

For this example, we want to disable the input element corresponding to the start date and display a message that the start date is disabled. This means we want to disable the field when the page loads; and therefore we want to insert our code inside the `onWindowLoad()` function. The external user exit function that allows us to do this is the `extPostOnWindowLoad()` function.

You can check the field names under the `payPlanMaintPlanPage's` Labels section.

    			    * Program name:      payPlanMaintPlanPage
    			    * Program location:  /ci/payPlan
    			    * Included XSL versions:
    			    *   common
    			    *   commonPage
    			    *   commonPageSingleRecord 3
    			    *
    			    * Labels:
    			    *     Table$Field  -  label   (element type, js_name)
    			    *     $PP_LBL  -  Pay Plan   (element type='L' , jsName='PP_LBL')
    			    *     ...
    			    * Widget Info:
    			    *     Widget_ID , Element Type - label info - label
    			    *     ...
    			    *     START_DT, IT - $START_DT -  Start Date

    			    *     PAY_METH_CD, IS - $PAY_METH_CD -  Pay Method
    			    *     ...

The two important pieces of information in this source view are:

The Program name definition - `payPlanMainPlanPage` in this example;

The Template file definition - `tabPage2.xsl` in this example.

Parent topic: Create an External User Exit