It adds a button in the window that allows to call a TCL procedure when necessary. The parameters are as follows,
n - Name used to reference the field, especially when writing the .dat file.
pn - Label that will be visualized by the user. It can be translated.
icon - It allows to put an image in .png format in the data tree. The image should be stored inside the images folder of the problem type.
proc - Permits to define a TCL proc. The code will receive an implicit argument with name 'domNode' that represents the TDOM node in the calling field context. Square brackets are not necessary in edit_command field.
help - It displays a pop-up window of help information related to the task the user is performing.