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 ];
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.
“Index Definitions” in this book
“Define and Build Indexes” in Defining a High-Performance Schema
“Introduction to Compiler Keywords” in Defining and Using Classes