widget-docstring
widget-docstring is a compiled Lisp function in `wid-edit.el
'.
(widget-docstring WIDGET)
Return the documentation string specified by WIDGET, or nil if none.
If WIDGET has a `:doc' property, that specifies the documentation string.
Otherwise, try the `:documentation-property' property. If this
is a function, call it with the widget's value as an argument; if
it is a symbol, use this symbol together with the widget's value
as the argument to `documentation-property'.