This class extends from FormField and models a single or multi-selection selector.
/**
* Returns tru if multiselect.
*
* @returns {boolean}
*/
isMultiple()
/**
* Returns the list of options of this field.
*
* @returns {DropdownFieldOption[]}
*/
getOptions()
/**
* Sets a value for this field.
*
* @param val
*/
setValue(val)
/**
* Removes a value from this field.
*
* @param val
*/
removeValue(val)
