Some of the tables in QuickBooks allow you to define your own fields. These fields are represented as the Custom Fields column. You can use this column to modify all your custom fields.
Custom fields are a special case with the driver. QuickBooks will only return custom fields if they have a value, and will return nothing if no custom fields are set. Custom fields are represented in XML like so:
<CustomField><Name>Custom Field Name</Name><Value>Custom Field Value</Value></CustomField>
To clear a custom field, submit the custom field name without a value. For instance:
<CustomField><Name>Custom Field Name</Name><Value></Value></CustomField>