The object category block is found in the Objects drawer of the Blawx toolbox.
The object category block is used to assert (or check) that an object is a member of a category.
The object category block is a statement block, and can be stacked with other statements.
The first internal connector expects an object or a variable. The second internal connector expects a category selector.
In a question or in the conditions of a rule or constraint, the block checks to see whether the object is a member of the category. In a conclusion or in a fact, it asserts that the membership is true.
Generally, in facts you will want to use the new object block, unless the object has already been declared as a member of a different category, and you are adding an additional category for that object.