10. Web.config Settings
The following line should be added to <controlSources> section in the web.config file:
<source mode="on" namespace="Sitecore.Shell.Extensions" assembly="CustomChecklist" prefix="contentExtension"/>
Sitecore.Shell.Extensions is the namespace in which the custom field is located.
assembly – is the name of the.dll file that contains the custom field.
prefix – this prefix will be used to identify your field.