[int_19h]

I think it's a reference to this:

"The operation is a conversion, such as the Object.ToString method."

But this only pertains to the conversion of the object on which the property is defined. In other words, you should have methods like ToString or AsEnumerable, rather than properties like String or Enumerable, even though other rules would indicate property to be valid (idempotent, fast, no arguments). This rule is just an indication that properties represent conceptual attributes of an object; and the result of a conversion of an object to something else is not an attribute.