When creating a new argument, it may be useful to ask the dictionary what entries are already set there, and conditionally create new entries based on those.
In this way, a template author can get additional logic through more advanced arguments.
Return information about the current DICT’s value for NAME. DICT is a dictionary, and NAME is a string that is the name of a symbol in the dictionary. This function derives values for some special NAMEs, such as FIRST and ’LAST’.