This MovableType plugin supplies a container tag of template which switches whether the specified value is contained in the array or hash variable. Now, you can describe the same logic with using the standard template tags, but its performance may not be desirable.
MTIsInArray / MTIsInHash conditional tagvalue is contained in the specified array or hash variable with name. When the array variable contains value, it may be true and variable __index__ is filled with its index number. When the hash variable contains value, it may be true and variable __key__ is filled with its hash key.
You can get the latest version and bug reporting is available in Trac repository.
日本語