the user chooses the second alternative, then the overall list has three
elements and the second and third must be strings.
+ The widgets can specify predicates to say whether an inline value
+matches the widget with the @code{:match-inline} element.
+
@node Type Keywords
@subsection Type Keywords
two arguments, a widget and a value; it should return non-@code{nil} if
the value is acceptable.
+@item :match-inline @var{function}
+@kindex match-inline@r{, customization keyword}
+Specify how to decide whether an inline value matches the type. The
+corresponding value, @var{function}, should be a function that accepts
+two arguments, a widget and an inline value; it should return
+non-@code{nil} if the value is acceptable. See @ref{Splicing into
+Lists} for more information about inline values.
+
@item :validate @var{function}
Specify a validation function for input. @var{function} takes a
widget as an argument, and should return @code{nil} if the widget's