CustomLinkInput

The custom linkinput control renders as a text box with a single select button.

Clicking the button will start a library action, which lets the user select a record. 
After confirming the selection, the primary key of the record is returned and put within the textbox.

Ctfp's

To use this control for a specific contenttype field, you must specify the ctfp cms:control and set its value to customlinkinput.

Which library to open must be specified using the ctfp cms:actioncode. Its value must refer to an existing Useraction's code.
The caption of the button must be specified using the ctfp cms:buttoncaption.

Both of these ctfp's are required when the customlinkinput control is used.