Internal (Index Keyword)
Specifies whether this index definition is internal (not displayed in the class documentation).
To specify that this index definition is internal, use the following syntax:
Index name On property_expression_list [ Internal ];
name is the name of the index. It is useful to follow a naming convention so that indices can be easily distinguished from properties. For example, you could include IDX at the end of all index names.
property_expression_list is either a single property name or a comma-separated list of properties, enclosed in parentheses.
Otherwise, omit this keyword or place the word Not immediately before the keyword.
Internal class members are not displayed in the class documentation. This keyword is useful if you want users to see a class but not see all its members.
If you omit this keyword, this index is displayed in the class documentation.